Abstract
Prefabricated floor element (1) having an elongated shape wherein a longitudinal direction (X), a transversal direction (Y), a height direction (Z), two end faces (11) which delimitate the element (1) in the longitudinal direction (X), two lateral faces (12) which delimitate the element (1) in the transversal direction (Y), a lower face (13) and an upper planar face (14) that delimitate the element (1) in the height direction (Z) are defined, which comprises transversal continuous upper grooves (15) on the upper planar face (14) or lateral grooves (26) on the lateral faces (24), the lateral grooves (26) extending from the lower tab (TS) to the upper planar face (24). The invention also relates to a structure comprising such prefabricated floor element (1) and further comprising a linear supporting element (LS) which supports one end of the prefabricated floor element (1) such that in the linear supporting element (LS) a supporting surface (51) is defined and a moment resisting system (MS) arranged on the linear supporting element (LS) and facing an end face (11) of the prefabricated floor element (1) and an upper concrete layer (LC) poured on top of the element (1) or in the shear key (SK) defined between two adjacent floor elements. The invention also relates to an installation for manufacturing the floor elements (1, 2).
Claims
1. Prefabricated floor element (1) having an elongated shape wherein a longitudinal direction (X), a transversal direction (Y), a height direction (Z), two end faces (11) which delimitate the element (1) in the longitudinal direction (X), two lateral faces (12) which delimitate the element (1) in the transversal direction (Y), a lower face (13) and an upper planar face (14) that delimitate the element (1) in the height direction (Z) are defined, characterised in that it comprises transversal continuous upper grooves (15) on the upper planar face (14).
2. Prefabricated floor element (1) according to claim 1, a lower tab (TL) on a lower edge of the lateral faces (12), and an upper tab (TS) on an upper edge of the lateral faces (12) the lower tab (TL) being longer than the upper tab (TS) in the transversal direction (Y).
3. Prefabricated floor element (1) according to claim 2, which comprises lateral grooves (16, 26, 36) on the lateral faces (12).
4. Prefabricated floor element (T1) according to claim 1, wherein the prefabricated floor element is a double-T floor element (T1), such that an upper planar plate (T11), and two vertical stems (T12, T13) extending downwardly from the upper planar plate (T11) are defined.
5. Prefabricated floor element (2) having an elongated shape wherein a longitudinal direction (X), a transversal direction (Y), a height direction (Z), two end faces (21) which delimitate the element (2) in the longitudinal direction (X), two lateral faces (22) which delimitate the element (2) in the transversal direction (Y), a lower face (23) and an upper planar face (24) that delimitate the element (2) in the height direction (Z) are defined, which comprises a lower tab (TL) on a lower edge of the lateral faces (22), characterised in that it comprises lateral grooves (26) on the lateral faces (24), the lateral grooves (26) extending upwards from the lower tab (TL) to the upper planar face (24), and which comprises an upper tab (TS) on an upper edge of the lateral faces (22)
6. Prefabricated floor element (1) according to any of the preceding claims, wherein the dimensionless thickness of the floor element cross section is below 0.6.
7. Structure comprising a prefabricated floor element (1) according to any of claims 1 to 4, which comprises: a linear supporting element (LS) which supports one end of the prefabricated floor element (1) such that in the linear supporting element (LS) a supporting surface (S1) is defined and: a moment resisting system (MS) arranged on the linear supporting element (LS) and facing an end face (11) of the prefabricated floor element (1), an upper concrete layer (LC) poured on top of the element (1), characterised in that it comprises armatures (AS) arranged along the longitudinal direction (X), such that a portion of the armatures (AS) is embedded in the concrete layer (LC) and another portion of the armatures (AS) extends such that they are embedded in the moment resisting system (MS), such that the armatures (AS), when acted under tension forces, can transmit forces to the concrete layer (LC), and the concrete layer (LC) can transmit forces to the prefabricated floor element (1) through the upper grooves (15) on the upper planar face (14), and then a negative moment is transmitted from the moment resisting system (MS) to the prefabricated floor element (1), wherein the moment resisting system (MS) is an upper extension of the linear supporting element (LS), a concrete poured between an upper extension of the linear supporting element (LS) and the end face (11), a concrete poured between the end face (11) and another prefabricated floor element arranged with its own end face facing the end face (11), or a concrete poured on top of the linear supporting element (LS) including reinforcement extending from its top to form a cast in situ torque moment resistant system.
8. Structure comprising two prefabricated floor elements (2) according to claim 5 or claim 6, the floor elements (2) being arranged adjacent such that a volume is defined therebetween the volume being filled with concrete such that a shear key (SK) is defined, which comprises: a linear supporting element (LS) which supports one end of the prefabricated floor elements (2) such that in the linear supporting element (LS) a supporting surface (S1) is defined and: a moment resisting system (MS) arranged on the linear supporting element (LS) and facing and end face (21) of the prefabricated floor elements (2), characterised in that it comprises armatures (AK) arranged along the longitudinal direction (X), such that a portion of the armatures (AK) is embedded in the upper portion of the shear key (SK) and another portion of the armatures (AS) extends such that they are embedded in the moment resisting system (MS), such that the armatures (AK) can transmit forces to the shear key (SK), and the shear key (SK) can transmit forces to the prefabricated floor element (2) through the lateral grooves (26) on the lateral face (24), and then a moment is transmitted from the moment resisting part (MS) to the prefabricated floor element (2).
9. Structure according to claim 8, which comprises armatures (VK) placed in the shear key (SK) and extending from the upper part to the lower part thereof, such that it allows the shear key concrete to withstand higher vertical shear stresses.
10. Structure according to any of claim 8 or 9, which comprises at least one duct (D) which extends continuously in the shear key (SK) and a post-tensioned tendon (PTT) inserted within the duct.
11. Structure according to claims 7 and 8.
12. Installation (IM1) for manufacturing prefabricated floor elements (1, 2, 3) according to any of claims 1 to 7 using dry concrete, which comprises: A formwork movable according to a longitudinal direction (X); The formwork comprising a front wall (I1), two lateral die walls (I2, I3), and an upper die wall (I4); A lower wall of the formwork being defined by the casting bed (F); A hooper (I5) having its lower outlet (I6) placed between the front wall (I1) and the upper wall (I4); An interior section mould (I7); characterised in that it comprises at least a rolling die (I8, I9, I10) placed after the formwork in the longitudinal direction (X), the rolling die having (I8, I9, I10) continuous surface teeth (I8T, I9T, I10T) having axial direction of the die (I8, I9, I10), the axis (8, 9, 10) of the die (I8, I9, I10) being perpendicular to the longitudinal direction (X), such that grooves (15, 16, 26, 36) can be formed on the lateral (12) or upper faces (14) of the prefabricated floor elements (1, 2, 3).
13. Installation according to claim 12, which comprises two rolling dies (I8, I9) having vertical axis and arranged after each lateral die wall (I2, I3), such that they allow to cast vertical continuous grooves in the prefabricated floor elements (2, 3).
14. Installation according to claim 12, which comprises a rolling die (I10) having a horizontal axis and arranged after the upper wall (I4), such that it allows to cast horizontal continuous grooves in the prefabricated floor elements (1, 3).
15. Installation (IM11) comprising a formwork elongated in a longitudinal direction (X), the formwork comprising a lower part (I21), and a removable upper part (124) having teeth (I24T) perpendicular to the longitudinal direction (X), such that grooves (15, 26, 36) can be formed on the upper faces (14, 24) of the prefabricated floor elements (1, 2, 3), characterised in that the removable upper part (I24) is formed by a plurality of former profiles (I24I) perpendicular to the longitudinal direction (X), the lower section (L24) of the former profiles (I24I) defining a decreasing section that defines the section of the grooves (15, 26, 36), the upper section (U24) of the former profiles (I24I) defining a constant section, the upper part (I24) further comprising joining profiles (I24B) having the longitudinal direction (X) and joined to an upper surface of the former profiles (I24I).
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0105] To complete the description and in order to provide for a better understanding of the invention, a set of drawings is provided. Said drawings form an integral part of the description and illustrate embodiments of the invention, which should not be interpreted as restricting the scope of the invention, but just as an example of how the invention can be carried out. The drawings comprise the following figures:
[0106] FIG. 1 shows a perspective view of the first variant of the prefabricated floor element, with upper grooves.
[0107] FIG. 2 shows a cross section parallel to transverse direction of a structural floor comprising two adjacent prefabricated floor elements of the first variant, with a shear key formed therebetween.
[0108] FIG. 3 shows a perspective view of the third variant of the prefabricated floor element, combination of the first and second variants of the prefabricated floor element, that is both with upper and lateral grooves.
[0109] FIGS. 4 and 5 show, respectively, an elevation view and a plan view of the first variant of a prefabricated floor element.
[0110] FIG. 6 shows a perspective view of the second variant of the prefabricated floor element, which only has lateral grooves.
[0111] FIG. 7 shows a cross section parallel to transverse direction of a structural floor comprising two adjacent prefabricated floor elements of the second variant, with a shear key formed therebetween.
[0112] FIG. 8A shows a perspective view of the first variant of the prefabricated floor element under the shape of a double T slab.
[0113] FIGS. 8B and 8C show, respectively, two variants of a prefabricated floor element with the same cross section, the element on the 8B including the transverse continuous grooves on the upper planar face, and the elements on 8C including the lateral grooves on the lateral faces.
[0114] FIG. 9A shows a plan of structural floor comprising several prefabricated floor elements at their bearing on a linear supporting element.
[0115] FIG. 9B is a detail of the plan view of FIG. 9A, showing a strut and tie forces diagram.
[0116] FIGS. 10A and 11A depict two inappropriate cross sections of a groove.
[0117] FIG. 10B depicts another inappropriate cross section of a groove.
[0118] FIG. 11B shows the proper shape and size that must have a grooveplaced on a lateral face or on an upper faceto function effectively.
[0119] FIG. 12 shows the proper shape and size that must have a lateral groove to function properly.
[0120] FIG. 13A shows the position of the Neutral Axis of the cross section of a prefabricated floor element, when the cross section is not cracked.
[0121] FIG. 13B shows the position of the Neutral Axis under Ultimate Limit State flexure forces of a floor structure including prefabricated floor elements.
[0122] FIG. 13C shows a side elevation one of the prefabricated floor elements and the armature, as if a cut was made in the middle of the concrete shear key and this concrete made transparent.
[0123] FIG. 13D shows a perspective view of a prefabricated floor element and the armature, with the concrete shear key made transparent.
[0124] FIG. 14A is a transversal section of a structural floor including two prefabricated floor elements including vertical lateral grooves and negative reinforcement placed in the concrete shear key. Lateral horizontal grooves are also depicted, which transfer vertical shear forces.
[0125] FIG. 14B is a longitudinal cross section of a structural floor including prefabricated floor elements and negative reinforcement placed in the concrete shear key; showing cracks in the shear key.
[0126] FIG. 15A is a longitudinal cross section of a structural floor including prefabricated floor elements, negative reinforcement, shear reinforcement and post-tensioning reinforcement, placed in a duct.
[0127] FIGS. 15B, 15C and 15D show elevations and cross sections of different possible shear reinforcements to be placed in the concrete shear key, in connection with negative armature, to prevent it from breaking.
[0128] FIG. 16A shows a perspective view of the structural floor, including prefabricated floor elements, armature to resist negative moments and a linear supporting element on top of which a moment resisting system should be, where the armature is embedded.
[0129] FIG. 16B shows a flexure moments diagram of a cantilever (all negative moments), that could be achieved with the structural floor depicted in 16A.
[0130] FIG. 16C shows a flexure moments diagram of a two span structure, with continuity over the bearing.
[0131] FIG. 17 shows a vertical section parallel to a prefabricated floor element in a structural floor, including also an armature embedded in the cast in situ topping.
[0132] FIG. 18 shows a detail of FIG. 17, where can be seen how compression forces transfer from the floor element to the cast in situ topping when a negative moment acts, rotating the floor element counter-clockwise.
[0133] FIG. 19 is similar to FIG. 17, but including the forces.
[0134] FIG. 20 is a typical scheme of the behaviour of a reinforced concrete element, under a negative moment.
[0135] FIG. 21 shows a vertical section according to a longitudinal direction of a prefabricated floor element in a structural floor, at shear key plane level.
[0136] FIG. 22 shows a vertical section according to a transversal direction of a prefabricated floor element in a structural floor.
[0137] FIG. 23 shows a vertical section according to a longitudinal direction of the structural floor, where the ends of the alveoli filled with cast in situ concrete are shown, as well as post-tensioned reinforcements placed in respective ducts.
[0138] FIG. 24 is a plan view of a floor having four elements which ends are resting on the linear support, and showing a number of solutions to counter-act lateral outward pushing forces.
[0139] FIG. 25 shows a vertical section according to a transversal direction of a prefabricated floor element in a structural floor, where the main forces are represented.
[0140] FIG. 26 shows a vertical section according to a transversal direction of a prefabricated floor element in a structural floor.
[0141] FIG. 27A shows a vertical section according to a longitudinal direction of a floor, in an arrangement where the moment resistant system is concrete poured between two facing prefabricated floor elements; with reinforcement properly anchored to both floor elements.
[0142] FIG. 27B shows a vertical section according to a longitudinal direction of a floor, in an arrangement where the moment resistant system is concrete poured between a vertical extension of the linear supporting element and the end of a prefabricated floor element; with reinforcement properly anchored to both floor elements.
[0143] FIGS. 28 to 30 show arrangements where the moment resisting system corresponds to a tie beam at the end of the floor.
[0144] FIGS. 31 and 32 show embodiments of the linear supporting element in combination with prefabricated floor elements having upper and lateral grooves.
[0145] FIG. 33 is a schematic plant view of the experimental arrangement used to test the inventive structural system.
[0146] FIG. 34 is Load vs Deflection plot where the curves for a prior art floor (PA) and the inventive system (IN) are shown.
[0147] FIG. 35 is a photo of an arrangement comprising two smooth prefabricated floor elements and an armature placed thereon, before pouring the top concrete layer.
[0148] FIG. 36 is a photo of an arrangement comprising two prefabricated floor elements according to the first variant of the invention, which comprises upper continuous longitudinal grooves, the linear supporting element and an armature placed thereon, before pouring the top concrete layer.
[0149] FIG. 37 is a photo of the experimental arrangement used for testing smooth prefabricated floor elements, that is, elements not including the inventive features.
[0150] FIG. 38 is a photo of an experimental arrangement used for testing the inventive floor elements.
[0151] FIG. 39 is a photo of an experimental arrangement used for testing the inventive floor elements, specifically at the end of the floor element where it rests on the linear supporting element where the upper grooves are clearly visible.
[0152] FIG. 40 is a photo of the floor made with the inventive prefabricated floor element under load.
[0153] FIG. 41 is a vertical section according to the longitudinal direction of an inventive installation used for manufacturing prefabricated floor elements according to the first variant.
[0154] FIG. 42 is a vertical section according to the transversal direction of the installation of FIG. 41.
[0155] FIG. 43 shows a perspective view of the rolling die used for imprinting the continuous upper grooves.
[0156] FIG. 44 is a vertical section according to the longitudinal direction of an inventive installation used for manufacturing prefabricated floor elements according to the second variant.
[0157] FIG. 45 is a vertical section according to the transversal direction of the installation of FIG. 44.
[0158] FIG. 46 shows a perspective view of the rolling die used for imprinting the continuous lateral grooves and the upper tabs on the prefabricated floor elements according to the second variant.
[0159] FIG. 47 is a vertical section according to the longitudinal direction of an inventive installation used for manufacturing prefabricated floor elements according to the third variant.
[0160] FIG. 48 is a vertical section according to the transversal direction of the installation of FIG. 47.
[0161] FIG. 49 is the experimental configuration of small tests for pure horizontal shear in the interface of precast floor elements and cast in situ topping
[0162] FIG. 50 is a picture of a specimen after the completion of a shear test like the one described in FIG. 49.
[0163] FIG. 51 is a Table with results of a series of shear tests like the one described in FIG. 49.
[0164] FIG. 52 is a plot summarizing the results of a series of shear tests like the one described in FIG. 49.
[0165] FIG. 53 is a conventional structural floor under construction, to be tested. The floor was completed only with concrete poured in the lateral joints a, and negative reinforcement, but no topping was poured.
[0166] FIG. 54 is a structural floor under construction, being prepared to be tested, including floor elements of the second variant (2), with lateral grooves (26).
[0167] FIG. 55 shows a completed structural floor, with floor elements of the second variant (2) under intense test loads.
[0168] FIG. 56 shows a Load-Gyration plot comparing the performance of the conventional floor (FIG. 53), named F3, and the floor made with floor elements of the second variant (FIGS. 54 and 55).
[0169] FIG. 57 shows a Negative Moment-Load plot comparing the performance of the conventional floor (FIG. 53), named F3, and the floor made with floor elements of the second variant (FIGS. 54 and 55).
[0170] FIG. 58 shows cracks, in a detailed view of the conventional structural floor previously shown in FIG. 53.
[0171] FIG. 59 shows a detail of the bearing of a floor element on a linear supporting element in the conventional structural floor previously shown in FIG. 53.
[0172] FIG. 60 shows, in a detailed view, important cracks appeared during the test performed on the conventional structural floor previously shown in FIG. 53.
[0173] FIG. 61 shows, in a detailed view, damages appeared during the test performed on the conventional structural floor previously shown in FIG. 53.
[0174] FIG. 62 shows a collapsed part of the conventional structural floor previously shown in FIG. 53, after the test had to be stopped, due to the failure.
[0175] FIG. 63 is a scheme of the experimental arrangement for a mid-size test done on structural floors including floor elements (2) with lateral grooves (26), to assess the importance of shear reinforcement (VK) placed within the cast in situ shear key (SK).
[0176] FIG. 64 is a picture of a specimen being tested with an experimental arrangement such as the one described in FIG. 63.
[0177] FIG. 65 shows a Load-Deflection plot of the tests performed on four specimens, after the experimental arrangement described in FIG. 63.
[0178] FIG. 66 shows different details of an alternative installation for casting the inventive floor elements.
[0179] FIG. 67 shows different details of another alternative installation for casting the inventive floor elements.
DESCRIPTION OF A WAY OF CARRYING OUT THE INVENTION
Description of the First Variant of the Invention
[0180] As shown for example in FIG. 1, according to a first variant, a prefabricated floor element is shown. This prefabricated floor element 1 has generally an elongated shape such that a longitudinal direction X, a transversal direction Y and a height direction Z are defined.
[0181] Throughout the following description, these directions will always be used with the same meaning.
[0182] By elongated it is meant that the length (dimension in the X direction) will be generally longer than the dimension in the transversal direction, i.e. the width, which in turn will be longer than the height (dimension in the Z direction). The height may also be referred to as depth, and in the context of shrinkage study, also as thickness.
[0183] Also two end faces 11 which delimitate the element 1 in the longitudinal direction X, two lateral faces 12 which delimitate the element 1 in the transversal direction Y, a lower face 13 and an upper planar face 14 that delimitate the element 1 in the height direction Z are defined.
[0184] FIGS. 4 and 5 show, respectively, an elevation view and a plan view of a particular embodiment of the first variant 1 of the prefabricated floor element, comprising transversal continuous grooves 15 on the upper planar face, but where the grooves are only present on two end portions, each covering of the entire length, such that the central portion is devoid of grooves. In this way the grooves are only in the places where they are useful, leaving the floor element unchanged and unweakened at the central portion. Having grooves only at the two end portions of the element is typically enough in most slabs, as at the ends of precast slabs where is placed negative reinforcement, and is there where is more intense the horizontal shear in the contact faces of precast concrete and cast in situ concrete.
[0185] An embodiment of this first variant where all the face 14 is covered with grooves 15 is advantageous, not for structural reasons, but for production reasons. It makes serial production more efficient as it allows an easy removing of the short segments of defective slab that occasionally appear during the casting process on the casting bed. The variant with grooves only at the ends may demand to reject bigger parts of the precast slab on the casting bed.
[0186] The prefabricated floor element 1 also comprises an upper tab TS on an upper edge of the lateral faces 12 the lower tab TL being longer than the upper tab TS in the transversal direction Y.
[0187] This element is advantageous when used in a structure as shown in FIGS. 16A, 17, 18, 19, 20, and 27A to 32. The optimum performance of the structure will be explained below with reference to FIGS. 36, 38, 39 and 40.
[0188] FIG. 16A shows a perspective view of the structural floor, including prefabricated floor elements 1 according to the first variant, with upper continuous grooves 15, an armature AS to resist negative moments an a linear supporting element LS on top of which a moment resistant MS system should be placed. The armature AS is embedded in a top concrete layer, which is not shown in this drawing. Within the topping, the armature AS will typically placed as high as possible, as long as the appropriate cover criteria are respected.
[0189] FIG. 2 shows a cross section parallel to transverse direction Y of a structural floor comprising two prefabricated floor elements 1 according to the first variant, which in turn comprise transversal continuous grooves 15 on the upper planar face 14, and displaying the main elements of the structural floor.
[0190] This arrangement gives rise to the moments as depicted in the following FIGS. 16B and 16C.
[0191] Specifically, FIG. 16B shows a flexure moments diagram of a cantilever (all negative moments), that could be achieved with the structural floor depicted in 16A. Said in other words, the end not shown in 16A of the prefabricated elements 1 can be either supported on another linear supporting element or not supported (cantilevered).
[0192] FIG. 16C shows a flexure moments diagram of a two span structure, with continuity over the central bearing and pinned unions on the two other bearings. This moments diagram could be properly resisted by a structural floor as the one depicted in 16A (if prefabricated floor elements were placed symmetrically at the other side of the linear supporting element LS. In particular, FIG. 16C clearly shows that the negative moment is raised at the linear supporting level, which in turn decreases the positive moment at midspan, thus allowing the system to withstand more loads.
[0193] FIG. 17 shows a section of a prefabricated floor element 1 placed in a structural floor, which includes also an armature AS embedded in the cast in situ topping LC. The floor element 1 is supported on surface 51 of the linear supporting element LS.
[0194] FIG. 19 is similar to FIG. 17, but including the stresses. The lower part of the floor element 1 compresses the concrete filling CF, while the upper portion of the floor element 1 acts upon the topping LS dragging it, thanks to the effect of grooves 15, and causing tension on the armature AS, represented by the left oriented arrows.
[0195] FIG. 18 shows a detail of FIG. 17, where it can be seen how compression forces are transferred from the floor element 1 to the cast in situ topping LS when a negative moment acts. FIG. 20 is a typical scheme of the behaviour of a reinforced concrete element, under a negative moment.
[0196] In FIGS. 27A to 32 are depicted several conventional variants of a moment resistant system MS wherein the negative reinforcement AS is embedded in order to guarantee the proper fixity to of the precast floor elements 1, 3 at their bearing.
[0197] FIG. 27A shows two floor elements 1 supported on a linear supporting element LS such as a wall, each of the floor elements 1, in combination with the topping LC and the concrete filling placed in between of both floor elements, acts as a moment resisting system MS of the other floor element 1. That is why, fixity is achieved by the fact that negative reinforcement AS is embedded in the topping LC at both sides of the axis of the linear supporting element LS.
[0198] FIG. 27B is similar to 27A, but in this case the linear supporting element LS is a precast beam, with a central protruding web. For the moment resisting system to work properly, the space between the web of the beam LS and the ends of the floor elements 1 must be filled with cast in situ concrete.
[0199] FIG. 28 shows a floor element 1 supported by a linear supporting element LS such as a wall. The moment resisting system MS is a cast in situ reinforced concrete tie beam, which includes hoops. Negative reinforcement AS is embedded in the moment resisting system MS to achieve a proper fixity of the floor element 1.
[0200] FIG. 29 is similar to 28. The main difference is that the wall LS includes a lateral wall, which enables the casting of the tie beam MS without the need of a lateral form.
[0201] FIG. 30 is similar to 28, but the linear supporting element LS is here a precast beam with a central protruding web. The beam, together with the concrete is cast in situ all around the web of the precast beam forms de moment resisting system MS, wherein the negative reinforcement AS is embedded to achieve the fixity of the floor element 1.
[0202] FIG. 32 is very similar to 27A, but in FIG. 32 floor elements 3 are of the third variant.
[0203] FIG. 31 shows a floor element 3 supported on a corbel of a linear supporting element LS that includes protruding negative reinforcement AS to be embedded in the topping LC. The moment resisting system MS is formed by the linear supporting element LS and the cast in situ concrete placed in between of the linear supporting element LS and the end face of the floor element 3.
[0204] The variants shown in FIGS. 8A and 8B, also provided with grooves on the upper surface, are other embodiments of the structural floor element that can work as shown up to now.
[0205] FIG. 8A shows a perspective view of the first variant of the prefabricated floor element under the shape of a double T slab T1, comprising transversal continuous upper grooves on the upper planar plate T11. There are two parallel vertical webs or stems T12, T13 joined to the upper planar plate T11 or flange, such that the double T section is obtained.
[0206] FIG. 8B shows another variant comprising the transverse continuous grooves 15 on the upper planar face 14, here referred as inverted-U slabs.
[0207] The armature has a diameter comprised between 10 and 20 mm, and the concrete layer LC has a height of at least 50 mm.
Description of the Second Variant of the Invention
[0208] FIG. 6 shows another variant of the prefabricated floor element 2 that has an elongated shape wherein a longitudinal direction X, a transversal direction Y, a height direction Z, two end faces 21 which delimitate the element 2 in the longitudinal direction X, two lateral faces 22 which delimitate the element 2 in the transversal direction Y, a lower face 23 and an upper planar face 24 that delimitate the element 2 in the height direction Z are defined, with a lower tab TL on a lower edge of the lateral faces 22, and it comprises vertical lateral grooves 26 on the lateral faces 24, the lateral grooves 26 extending from the lower tab TS to the upper planar face 24.
[0209] Therefore the difference with the first variant is that the grooves are lateral.
[0210] The prefabricated floor element comprises a lower tab TL on a lower edge of the lateral faces 22, the lower tab TL being longer than the upper tab TS in the transversal direction Y.
[0211] An alternative embodiment of this second variant can be seen in FIG. 14A, where the upper tab TS is replaced by a longitudinal groove LG on the faces 22.
[0212] Like in the first variant, and as shown in FIG. 6, in a preferred embodiment the lateral grooves 26 are present only on two end portions, each covering of the entire length, such that the central portion is devoid of grooves. In this way the grooves are only in the places where they are useful, leaving the floor element unchanged and unweakened at the central portion.
[0213] As shown for example in FIGS. 7, 9A, 14B, 21 to 26, this prefabricated floor element 2 is destined to be arranged adjacent to another floor element 2 in the transversal direction and then both supported at their ends on two linear supporting elements LS, like walls or beams arranged in the transversal direction Y. Specifically, these elements 2 allow, by arranging an armature AK in the upper part of the shear key SK formed by pouring concrete in the volume delimited by the lateral faces and the tabs and extending beyond the end faces 21, to transmit tension forces having the longitudinal direction X thanks to the lateral grooves 26. These tension forces in the armature SK, in combination with the compression forces acting upon the lower part of the end faces 21 allow then to transmit negative moments through said face, these moments being around an axis in the Y direction.
[0214] FIG. 7 shows a cross section parallel to transverse direction Y of a structural floor comprising two prefabricated floor elements 2, comprising lateral grooves 26 on the lateral faces 22, the lateral grooves 26 extending from the lower tab TL to the upper face 24, and displaying the main elements of the structural floor.
[0215] Description of the Flexure Strength Mechanism
[0216] FIG. 13C shows a side elevation of one of the prefabricated floor elements 2 and the armature AK, as if a cut was made in the middle of the concrete shear key SK and this concrete made transparent. Beside the elevation are depicted the strain scheme and the section equilibrium scheme. The least includes both stresses and forces.
[0217] FIG. 13D shows a perspective view of a prefabricated floor element 2 and the armature AK, while the concrete shear key SK is made transparent. The figure explains how when the armature AK is under tension, it drags the concrete shear key SK, which in turn exerts a compression F.sub.SK on the prefabricated floor element 2. Compression stresses .sub.SK are depicted on the floor element 2. It is relevant to note, as it can be seen in FIG. 13D, that the lateral surface of the groove is essential for the proper functioning of this solution, and it has an especial importance the part of this surface which is near the top surface (24). Also, the effectiveness of the reinforcement AK depends directly on its position in height. That is why it must always be placed as high as possible while respecting the appropriate cover criteria.
[0218] When prefabricated floor elements do not have a topping, negative reinforcement is placed at the sides of each floor element, in the relatively narrow cavities CC filled with concrete between floor elements 2, which forms a negative-moment-resistant rib or shear key SK. This means most of the load of the floor is applied directly on the prefabricated floor element, and only a small part is directly applied on the rib of shear key SK. However, the prefabricated floor elements are not directly fixed, so not negative-moment-resistant. This situation tends to lead the floor elements more loaded to deflect as a pinned-pinned element, while the cast in situ rib or shear key SK deflects much less, just as a fixed-fixed element does. As there is a shear key, upper tab TS or longitudinal groove LG, transmitting vertical shear forces in the vertical faces 22 of the precast floor element, the differential deflection is prevented. As a result prefabricated floor elements equal their deflection to that of the cast in situ rib or shear key SK. This happens thanks to the fact that the floor elements hang on the rib or shear key SK. This hanging means an important transfer of load form the floor element to the rib or shear key SK, leading this rib to withstand important shear forces. Reinforcement is necessary for the rib not to break under this important shear forces. Thus, if negative reinforcement is added only within the ribs, as there is no topping to place those negative reinforcements, shear reinforcement is also required in order to withstand the considerable shear load transfer from the floor elements to the rib or shear key SK.
[0219] FIG. 13A shows the position of the Neutral Axis NA of the cross section of a prefabricated floor element 2, when the cross section is not cracked.
[0220] FIG. 13B shows the position of the Neutral Axis NA under Ultimate Limit State flexure forces of a floor structure including prefabricated floor elements 2. In the case depicted, the floor structure is under a negative moment. In this situation, only the lower part of the cross section of the prefabricated floor elements (hatched) is under compression, while the rest of the cross section is under tension. In the middle, the armature AK is under tension.
[0221] On the one hand, the fact that the neutral axis under Ultimate Limit State ULS is so low for negative moments, and on the other hand the fact that in the variant 2 the lateral faces 22 are the only contact surfaces between cast in situ and precast concrete able to transfer negative moments from floor elements 2 to the negative reinforcement, explain the importance that the lateral (vertical) grooves 26 are made as big as possible: extending them from the lower tab TL to the upper planar face 24.
[0222] Description of Unwanted Obliquus Forces and Their Remedy
[0223] FIG. 9A shows a plan of structural floor comprising several prefabricated floor elements 2 at their bearing on a linear supporting element LS, displaying also the negative armatures AK placed within the concrete filled shear key SK. Compression forces parallel to transversal direction Y are displayed, such as the ones acted by a transversal post-tensioned armature.
[0224] FIG. 9B is a detail of the plan view of FIG. 9A. On this 9B figure a tie and strut scheme is superposed to the main elements of the structure. On the armature AK one can see a tie with an increasing tension force. This tension force on the armature AK is increased by the compressions (struts) exerted by the prefabricated floor elements 2, through the lateral grooves and into the shear key SK. The system is in equilibrium by causing tensions (and cracksdepicted as undulations) on the linear supporting element LS. These diagonal compressions are perpendicular to maximum tensions that tend to cause cracks on the upper planar face 24 of the floor element 2. Both the cracksdepicted as undulationson the linear supporting element LS and those on the upper planar face 24 of the floor element can be remediated by compression forces parallel to the transverse direction Y, such as forces exerted by post-tensioning.
[0225] FIG. 24 is similar to 9A but shows at the left side hollow core elements cut at mid of their height. In this figure are depicted four alternative or complementary solutions to control diagonal cracking in the upper planar face 24, and to prevent lateral displacement of precast floor elements placed at the perimeter of the structural floor. Notice that this sort of failure is not relevant in interior floor elements, as those are already confined. So, the four mentioned solutions are: 1) Post-tensioning in the direction parallel to the linear support element; 2) Post-tensioning by placing a tendon in each shear key SK; 3) Tie beams placed in the perimeter (upper and lower parts of the figure); 4) Grooves of teeth blocking lateral movement. In the case depicted FIG. 24 is shown a solution consisting in filling with cast in situ concrete a small length of all alveoli. This is achieved by slightly recessing each plug (T) into its alveolus.
[0226] Description of the Vertical Shear Strength Mechanism of the Rib or Shear Key SK
[0227] FIG. 14A shows a detail of a structural formed by two floor elements 2 with lateral vertical grooves and lateral horizontal grooves SG. Between the two floor elements, a shear key SK is formed with cast in situ concrete, including AK reinforcement embedded therein. As mentioned above, as typically pinned-pinned floor elements 2 tend to deflect more than the cast in situ rib or shear key SK, they try to deflect downwardly (as big downward arrows suggest in FIG. 14A), but thanks to horizontal grooves SG which act as vertical shear keys, the downward deflection of precast floor elements is prevented and an intense vertical shear force is transferred to the cast in situ rib or shear key SK. So, precast floor elements hang on ribs SK.
[0228] The variant shown in FIG. 8C is, also provided with grooves 26 on the lateral faces 22. This embodiment and other similar embodiments of the structure can work as shown according to the second variant of the invention.
[0229] FIG. 14B shows a longitudinal section of a structural floor including prefabricated floor elements 2 and negative reinforcement AK placed in the concrete shear key SK. This figure shows the behaviour that would have the floor in the case that prefabricated floor elements 2 would not have an upper tab TS nor a side groove SG: the prefabricated floor element would deflect more, as a pinned-pinned element, and the concrete shear key SK would deflect much less, as a fixed-fixed.
[0230] FIG. 14C is a longitudinal cross section of a structural floor including prefabricated floor elements 2 and negative reinforcement AK placed in the concrete shear key SK. Cracks are depicted, which appear in the concrete shear key SK due to the intense vertical shear force, due to the fact that floor elements 2 tend to hang on the shear key SK, as illustrated in 14A.
[0231] In some case such as the depicted in FIGS. 15A, 21 and 22, the structure comprises armatures VK placed in the shear key SK and extending from the upper part to the lower part thereof, such that it allows the concrete shear key to withstand typically high vertical shear stresses.
[0232] FIG. 15A is a longitudinal cross section of a structural floor including prefabricated floor elements 2, negative reinforcement AK, shear reinforcement VK and post-tensioning PTT reinforcement, placed in a duct D. No cracks appear, as the concrete shear key SK properly withstands the intense vertical shear forces, thank to proper reinforcements.
[0233] Placing post-tensioning PTT in the shear key SK has the additional advantage to prevent cracks in the upper planar surface 24, such as the ones depicted in FIGS. 9B, 24 and 60, which very much increases the stiffness of the whole floor, reducing its deflection.
[0234] FIG. 21 shows a section parallel to a of a prefabricated floor element 2 in a structural floor, cutting the structural floor through the concrete shear key SK. Shear reinforcement VK is included. This floor does not include post-tensioning PTT, as it may not be necessary in cases where loads on the floor are not intense.
[0235] FIG. 22 shows a structural floor in a section transverse to prefabricated floor elements 2 with lateral grooves 26, including a cast in situ shear key SK and both flexure reinforcement AK and shear reinforcement VK embedded within the shear key SK. In this sort of floor elements 2, the bottom tab TL is typically bigger than in currently conventional floor elements. This increase in the size of bottom tabs TL is intended to increase de the width of the cast in situ shear key SK, as this is the only place where to place negative reinforcement SK, shear reinforcement VK and post-tensioning reinforcement PTT (if any). Moreover, as it is the only place where the whole armature can be placed, forces are typically very concentrated, and reinforcement bars have big diameters. It is not unusual to use 1 or 2 rebars of 20 mm or 25 mm of diameter put side by side, plus a shear reinforcement with 8 mm to 12 mm of diameter. Of course, proper cover concrete must be guaranteed all around the rebars. As a result, the average width of the shear key SK will hardly be smaller than 100 mm.
[0236] FIG. 23 shows a section parallel to a prefabricated floor element 2 in a structural floor, cutting the structural floor through an alveolus in the floor element 2. A plug T, intended to block the entrance of cast in situ concrete in the hollow core slab, is intentionally slightly recessed into the alveolus, to let cast in situ concrete fill the end of the alveolus.
[0237] FIGS. 15B, 15C and 15D show elevations and cross sections of different possible shear reinforcements to be placed in the concrete shear key SK, in connection with negative armature AK, to prevent the concrete shear key SK from breaking due to intense vertical shear loads, just as shown in FIG. 62. 15B shows typical stirrups. 15D shows Z-shaped shear reinforcement. 15D shows shear studs.
[0238] FIG. 3 shows a perspective view of the third variant of the prefabricated floor element 3, combination of the first 1 and second 2 variants of the prefabricated floor element, comprising transversal continuous upper grooves 15 and lateral grooves 36 on the lateral faces.
Details Regarding the Grooves
[0239] FIGS. 10A and 11A depict two inappropriate cross sections of a groove. When the reinforcement is put under tension, it pulls the cast in situ concrete (hatched), and the inappropriate shape of the groove will tend to separate the precast concrete (in white) of the cast in situ concrete. 10A depicts a rounded shape of the cross section; and 11A a side face of the groove excessively inclined (more than 10)
[0240] FIG. 10B depicts another inappropriate cross section of a groove. This shape of the precast element virtually makes impossible a properly consolidation of precast concrete. Moreover, it is very hard (or impossible) to unmould. If these difficulties were solved, the shape would tend to easily break (as depicted) when the reinforcement pulled the cast in situ concrete.
[0241] FIG. 11B shows the proper shape and size that must have a grooveplaced on a lateral face or on an upper faceto function effectively. The inclination of the lateral faces of the groove should not deviate more than 10 from the perpendicular to the direction to the shear force (typically parallel to the contact surface between the precast element and the cast in situ concrete). The depth dg of the groove should not be less than 1 time the diameter of the biggest aggregate of the cast in situ concrete. The width wg of the groove, measured parallel to the longitudinal direction X, should not be less than 1.5 times the diameter of the biggest aggregate of the cast in situ concrete.
[0242] FIG. 12 shows the proper shape and size that must have a lateral groove to function properly. The values for the depth dg and the width of the groove wg are those already defined. The vertical dimension must go from the lower tab TL to the upper face 24.
[0243] The minimum sizes mentioned above are aimed at effectively preventing the slipping of the concrete cast in the job from its place on the prefabricated element. This is achieved on the one hand by ensuring the correct filling of the grooves by the poured concrete; and on the other hand by ensuring that the shear forces act upon the aggregate, and not only on the cement matrix wrapping the aggregate; in order to avoid that the aggregate of the cast in situ concrete detaches from its cement matrix. Typical diameter of biggest aggregates ranges from 10 mm to 20 mm. Thus, the height and width must be at least of 10 mm and 15 mm, respectively; but 20 mm and 30 mm, respectively, are generally recommended in order to cover a bigger range of aggregate sizes with the same geometry of the grooves. Respecting these criteria, guarantees an ultimate mode of failure in which either the concrete of the cast in situ concrete or the precast member breaks under shear; but never a failure happens in the interface (separating both concretes). This second sort of failure is not desired, as it is very difficult to predict, as it depends on a number of aleatory factors (humidity history, temperature history, direct insolation, wind, dirt in the job, rain in the job) or of factors that are almost impossible to control from one job to another (formulation of cast and degree of compaction of cast in situ concrete; age of precast members when cast in situ concrete is poured, etc.). These factors will have a very strong influence in the differential shrinkage a differential stiffness of the two concretes. Moreover, the influence of a number of these factors on the interface shear strength of the junction is not even described in most common codes, which mainly base their formulas on principles of cohesion-adhesion of the interface. So, a proper prediction of the strength of this interface surfaces is extremely hard to achieve.
[0244] On the contrary, when deep grooves are available, that guarantee an ultimate mode of failure causing the rupture of one of the two concretes (rather than the interface) allows for a very good prediction of the actual strength of the junction. This is because the ultimate shear strength of concrete (one sole material) is very well known and well described in codes. It only depends on the tension strength of concrete, which in turn depends on its compression strength. Thus, none of the mentioned aleatory factors enter into play.
[0245] Spacing between grooves should preferably be proportional to the width of the groove. The relation of spacing of grooves to width of grooves must be similar to the relation of shear (or tension) strength of precast concrete to the shear (or tension) strength of cast in situ concrete. (Shear strength of plain concrete is considered here to be proportional to tension strength.) When this proportionality is respected both materials will break at the same time. This means, nor the precast concrete teeth (protrusions placed between each pair or grooves) nor the cast in situ concrete teeth (formed when filling in the grooves) are clearly weaker that its counterpart, avoiding weak points in the junction that would lead to lowering the horizontal shear strength of the junction.
Description of Experimental Results of Horizontal Shear Strength and its Relation with Differential Shrinkage
[0246] A series of tests have been performed to assess the horizontal shear strength of different geometries of the contact surface of a precast floor element and a topping cast on top of it. Three sort of tests have been performed: a) Tests with small specimens under pure horizontal shear (35 tests); b) Tests with midsize specimens under horizontal shear induced by bending (6 tests); c) Big size specimens under horizontal shear induced by bending (2 tests).
[0247] The different sorts of tests gave consistent results. Next are also described the results of tests with small specimens, as those are the more representative.
[0248] Five sorts of surfaces have been tested: [0249] 1) Smooth surface (FIGS. 51 and 52) [17 specimens +2 medium size specimen+1 big specimen] [0250] 2) Brushed surface, with scratches shallower than 2 mm (FIGS. 51 and 52) [2 specimens] [0251] 3) Surface with holes, 2 cm deep (FIGS. 51 and 52) [4 specimens+2 medium size specimen] [0252] 4) Surface with shallow transverse grooves, 1 cm deep (FIGS. 51 and 52) [2 specimens] [0253] 5) Surface with appropriate transverse grooves, 2 cm deep (FIGS. 51 and 52) [10 specimens+2 medium size specimen+1 big specimen]
[0254] The two most studied cases are smooth surfaces (batch 1) and surfaces with appropriate transverse grooves (batch 5); also the case with holes (batch 3) has been studied. In all these cases, different concretes have been tested at different ages. These different concretes and ages have been designed to lead to different differential shrinkages, in order to assess the influence of this phenomenon on the horizontal shear strength.
[0255] FIG. 49 shows the layout of the pure horizontal shear test, on small specimens. The precast floor elements used are segments of hollow core slabs. The dimensions are in mm. Two smooth floor elements 31 are arranged facing each other but spaced 40 mm apart with a gap G1. A horizontal plate 32 is arranged in the joint and then a topping layer 33 is poured. Next, a weight 34 is applied above the level of the joint, to prevent lifting of the floor elements 31. At the free ends of the plates, vertical pressure plates 35 are arranged, through which a tensioning armature 36 is passed. In this way the forces P can be applied at the right end, that is to say that the armature is pulled by bearing on the pressure plate 35. This causes the floor elements to be brought closer and the behaviour of the joint between the compression layer 33 and the smooth floor element 31 can be determined at the level of the interface between both.
[0256] FIG. 50 is a picture of a specimen with smooth contact surface just after the pure horizontal shear strength test has been completed. The bond is completely broken and the topping has slipped from its original place.
[0257] FIG. 51 is a table including the results of the small scale tests. Horizontal shear strengths indicated in the table are average values of each series of tests. So the complete series of results includes strengths clearly above and under these average values.
[0258] FIG. 52 is a chart showing the ranges of shear strengths obtained in small tests
[0259] Seeing all the results leads to the next conclusions: [0260] i) There is a very noticeable dispersion in the results. [0261] ii) The dispersion in the results can be partially explained by putting together tests where differential shrinkage is very different. Indeed, the dispersion due to differential shrinkage (which is not described here in detail) makes it clear that differential shrinkage has an important influence in modifying the shear strength of the joint. [0262] iii) If we compare only the worst strength results of each sort of contact surface it is seen that smooth surfaces and brushed surfaces (only 2 specimens) have a neglectable shear strength, and that surfaces with holes have a minimum shear strength of 0.20 MPa; while surfaces with grooves (no matter their depth) have in all cases strengths over 0.75 MPa. [0263] iv) If we supress from the series of the results, those of the worse concrete for topping, the minimum shear strength of grooves of the proper depth rise to 1.00 MPa; while minimum strengths for smooth surfaces do not improve.
Description of Experimental Results for the First Variant
[0264] The prefabricated elements according to the first variant were successfully tested as described in this section.
[0265] FIG. 33 is a schematic plan view of the experimental arrangement, which comprises: [0266] The actuators (ACTUADOR 1, ACTUADOR 2) are hydraulic jacks that apply vertical loads on each of the two spans, with an arrangement which simulates , with reasonable precision, a uniform superficial load; [0267] The cells (CLULA 1, CLULA 2, CLULA 3, CLULA 4) are load cells that indirectly measure the vertical reaction of the linear supporting element placed at the central part of the experimental arrangement;
[0268] SG1, SG2 . . . are the strain gauges for measuring the elongations;
[0269] Upper Gauges SGA and SGB measure the upper surface elongations on the upper end portions of the slabs;
[0270] To make a valid comparison with the systems of the state of the art, the experimental arrangements of FIGS. 35 and 36 were used. The FIG. 35 arrangement is a system with flat hollow core slabs, that is to say conventional, where negative reinforcement has been placed in the topping, which is unusual in conventional practice. That has been done to put in evidence why negative reinforcement is not effective (and thus not used) in conventional practice. On the other hand, that of FIG. 36 is an installation including floor elements (in particular hollow core slabs) such as those of the present invention.
[0271] A detail of the structure of FIG. 35 is shown in FIG. 37, whereas a detail of the structure of FIG. 36 is shown in FIG. 38, which clearly shows a groove 15 filled with concrete. FIG. 39 allows to appreciate the upper concrete layer LC (topping) which fills the upper grooves 15 of a floor element 1.
[0272] FIG. 34 shows the comparative load-deformation plots between the floor system with hollow core slabs with conventional layer (including negative reinforcement) as shown in FIG. 35 (curve PA) and a system according to the present invention (IN), shown in FIG. 36. Here it is clearly seen that the maximum ultimate load in the first case (PA) is 295 kN, while using the system of FIG. 16A, (corresponding to the moment diagram 16C), a maximum ultimate load value of 480 kN is obtained. It can also be seen that in the plot corresponding to an assembly according to the conventional technique (PA) bonding is already broken at 240 kN and from this load on the floor behaves simply as a hollow core slab; which only includes positive moment reinforcement. Thus, no proper bonding exists between the precast floor element and the topping, where the negative reinforcement is embedded. Under the load of 240 kN, when the bonding breaks, the maximum horizontal shear stress is 0.28 N/mm.sup.2, and the average horizontal shear stress on the contact face of precast concrete and cast in situ concrete is 0.14 N/mm.sup.2. This is totally consistent with small scale tests for horizontal shear strength.
[0273] The photo of FIG. 40 shows a floor according to the invention subjected to a load of 483 kN per actuator (hydraulic jack), where the continuous upper grooves are appreciated. It is seen that even in these extreme conditions the prefabricated part is still in good condition. Under the load of 483 kN, when the structural floor reaches ULS under flexure, bonding on the contact surface is totally intact. Under this load, the peak horizontal shear stress on the contact face of precast concrete and cast in situ concrete is 0.57 N/mm.sup.2, the average horizontal shear stress on the grooved zone (end of the length) is 0.38 N/mm.sup.2; and the average horizontal shear force on the central of the slabs is 0.10 N/mm.sup.2. The stresses values on the grooved zone are 1.40 times and 2.11 times, respectively, smaller than the minimum horizontal shear strength (0.80 N/mm.sup.2) of joints of the topping and precast elements with grooves as those defined in this invention, when de topping is made with the worst concrete of those included in the tests. These values are the security coefficient of the junction of the tested structural arrangement (FIG. 33). This security coefficient can go up to 1.75 times and 2.63 times, respectively, when we consider the minimum horizontal shear strength (1.00 N/mm.sup.2) of joints where the second worse concrete is used for the topping.
[0274] In most common practice floors peak horizontal shear stress will be under 0.35 N/mm.sup.2. This corresponds to average stresses of 0.23 N/mm.sup.2 when grooves are only on the last of floor elements, and to 0.175 N/mm.sup.2 when grooves cover the hole floor element. Only under. extremely severe conditions may the peak horizontal shear stress go up exceptionally to 0.50 N/mm.sup.2. In all these cases the safety coefficients are summarized in the next table.
TABLE-US-00002 SECURITY COEFF. Second FACTORED HORIZONTAL SHEAR STRESS (N/mm.sup.2) worse Worse [.sub.d = 1.4* .sub.k] concrete concrete Highest Factored peak stress 0.35 2.86 2.23 stresses in (end of the slab) conventional Factored average stress 0.23 4.29 3.43 situations (grooves only at end of the slab) Factored average stress 0.175 5.71 4.57 (grooves all over the slab) Highest Factored peak stress 0.50 2.00 1.60 stresses in (end of the slab) extreme Factored average stress 0.33 3.00 2.42 situations (grooves only at end of the slab) Factored average stress 0.25 4.00 3.20 (grooves all over the slab)
[0275] Watching the results in the table, it can be seen that the solution with grooves is sufficiently secure in all cases, independently of the sort of concrete used for the topping.
Description of Experimental Results for the Second Variant
[0276] The prefabricated elements according to the second variant were tested as described in this section, and showed a much better performance than a floor made with conventional precast floor elements.
[0277] The experimental arrangement to test the floor elements of the second variant is very similar to that of the first variant. So that the schematic experimental arrangement showed in FIG. 33 is appropriate to describe the tests of the second variant.
[0278] To make a valid comparison with the systems of the state of the art, the experiment was performed on the floors shown in FIG. 53 (conventional floor elements) and in FIG. 54 (second variant floor elements). Notice how in FIG. 54 floor elements 2 have lateral grooves 26, while conventional floor elements in FIG. 53 have smooth lateral faces, very badly suited (or totally unable) to transfer shear forces parallel to the longitudinal direction.
[0279] FIG. 55 shows a structural floor including floor elements 2 with lateral grooves 26, under heavy load.
[0280] FIG. 56 Shows the Load-gyration plot of the two structural floors tested, corresponding to a first cycle of load. F3 is for the conventional floor, and F4 is for the structural floor with floor elements 2 with lateral grooves 26. After this plot, at a first impression the two floors seem to have a very similar performance. However, after it is clearly appreciated that the F4 performs much better than F3. It is pointed out that the transverse confinement would yield even better results.
[0281] FIG. 57 shows the Negative Moment-Load plot. The negative moments of this plot has been computed from the reactions on the load cells placed under the linear support element where all floor elements are supported. From this plot, it can be seen a very different behaviour of the two structural floors. F3, the conventional structural floor, behaves very poorly, when compared to F4, which includes floor elements 2 with lateral grooves 26. For the floor F4, the resisted negative moment increases almost linearly as load increases. For a load of 200 kN, the negative moment is 111 kN.Math.m; while for the same load, the negative moment is 21 kN.Math.m for the floor F3 (which is less than 5 times the negative moment resisted by F3). This big difference puts in evidence that conventional floors are almost unable to withstand negative moments, and work almost as pinned-pinned floors, even when they include considerable negative reinforcement.
[0282] The plot of FIG. 57 also explains why the behaviour of the two floors seems so similar, when reading the Load-Gyration plot (FIG. 56). In FIG. 57, it is seen that when the load on the F4 goes beyond 200 kN, the negative moment increases very slowly, and when the load goes beyond 278 kN, the negative moment is abruptly reduced to 81 kN.Math.m. These two behaviours, but mostly the decrease in negative moments beyond the load of 278 kN, indicates an inappropriate behaviour of the floor: the negative reinforcement ceases to work properly. This improper behaviour is due to a certain slipping of the negative reinforcement AK from the concrete of the rib or shear key SK. This slipping is due to a loss of bonding due to a longitudinal crack along the reinforcement AK, caused by the lack of lateral confinement of the floor elements. It is to be noticed that the bonding failure occurred for a load very near to the yielding load of the negative reinforcement (estimated to occur for a load of 280 kN.Math.m); which means that even without lateral confinement, the structural floor F4 was about to function properly and reach its negative moment-strength peak. This malfunction of the tested specimen F4 lead it to a behaviour, at the end of the test, similarly to a pinned-pinned floors, thus similarly to conventional floors. This explains why in FIG. 56 both floors reach similar maximum loads.
[0283] FIG. 58 shows how in slab F3, conventional structural floor, longitudinal cracks CR appear all along the contact junction of precast floor elements and the cast in situ rib. These cracks appear already for very low loads during the test. Moreover, in the figure, which is taken when the floor is under a load of 100 kN approximately, a transverse crack TCR cutting the cast in situ rib can be seen. These cracks coincide quite exactly with the point where the negative bar ends (indicated with a line L on the floor element). This sort of transverse crack, combined to the cracks in the longitudinal direction, shows clearly that the cast in situ rib (with the negative reinforcement embedded therein) has detached from the precast floor elements, and slipped. This cracks, and their associated loss of negative strength of the structural floor, are totally consistent with the Negative Moment-Load plot of F3 (FIG. 57), where beyond the load of 100 kN the floor is almost unable to withstand more negative moments.
[0284] FIG. 59 shows how structural floor elements, which are not laterally confined, move laterally during the test. This lateral movement is noticeable by the fact that the elastomeric band EB locally is uplifted.
[0285] FIG. 60 shows severe damage in floor elements and cast in situ ribs, in the test with conventional floor elements. Diagonal cracks in the slabs are parallel to maximum compression forces (struts) due to a certain (small) negative moment strength of the floor.
[0286] FIG. 61 shows the cast in situ ribs SK uplifted in comparison to the floor elements. This behaviour occurs due to two related phenomena. Firstly, the differential deflection of the floor elements (acting as pinned-pinned elements) and the cast in situ rib (acting as a cantilever) and secondly the lack of proper shear reinforcement to enable the cast in situ rib to resist the strong vertical shear force due to this differential deflection.
[0287] FIG. 62 shows the catastrophic state in which ended the structural floor F3, after finishing abruptly, due to a fragile vertical shear failure of the floor element. The picture shows also important vertical shear cracks in the rib. This failure is a proof of how insecure is reinforcing and loading a conventional structural floor as if it was able to withstand negative moments. Another series of tests have been performed to assess the importance of placing shear reinforcement in structural floors including floor elements 2 with lateral grooves 26. FIG. 63 shows the experimental arrangement to assess the shear strength of the cast in situ ribs. To facilitate the test, the structural floor has been completely reversed, so that the loads exerted downwardly by the hydraulic jacks HJ on the floor are simulating the upward reaction exerted by the linear supporting element supporting two lateral spans of a structural floor. So, the prefabricated floor elements 2 are reversed (with the prestressed reinforcement in the upper face), and the reinforcement AK of the cast in situ shear key SK is placed in the bottom face, and thus resists moments causing tension in the lower face.
[0288] FIG. 64 shows a specimen deflecting under intense test load applied with the experimental arrangement depicted in FIG. 63.
[0289] The experimental arrangement of FIG. 63 and FIG. 64 comprises: [0290] The actuators, that are hydraulic jacks HJ that apply vertical loads at the two ends of the central tie beam, with an arrangement which simulates, with reasonable precision, the reversed moments diagram on a linear bearing supporting two symmetrical spans under a uniform superficial load; [0291] SG1, SG2 . . . are the strain gauges for measuring the elongations on the floor elements, on the shear key and on the central tie beam (which simulates the linear supporting element); [0292] LVDT-1, LVDT-2 are gauges on supports, to measure the vertical deflection of the specimen
[0293] FIG. 65 shows the Load-Deflection plots of 4 tests performed with the arrangement described in FIG. 63 and FIG. 64. All the specimens were identical in all details, but two of them (F1 and F3) did not include vertical shear reinforcement VK embedded in the cast in situ shear key SK. None of the specimens led the reinforcement AK of the shear key to yielding. A very high amount of reinforcement AK was placed to achieve this result, to find other failure modes. The two specimens including shear reinforcement F2, F4 achieved a maximum load of 105 kN. This is a 21% more than the maximum load achieved by F1 (86 kN) and F3 (88 kN), which did not include shear reinforcement VK. Both these results, and the brittle shear failure of the floor shown in FIG. 62 show the importance of placing shear reinforcement VK in shear keys SK in this sort of floors.
Description of Installations Destined to Manufacture the Inventive Floor Elements
[0294] Movable Formwork for Dry Concrete Precasts
[0295] As shown in FIGS. 41 a 48, the invention also relates to installations IM1, IM2, IM3 for manufacturing prefabricated floor elements 1, 2, 3 according to any of claims 1 to 6 using dry concrete, which comprises: [0296] A formwork movable according to a longitudinal direction X; [0297] The formwork comprising a front wall I1, two lateral die walls I2, I3, and an upper die wall I4; [0298] A lower wall of the formwork being defined by the casting bed F; [0299] A hooper I5 having its lower outlet I6 placed between the front wall I1 and the upper wall I4; [0300] An interior section mould I7 which extends longitudinally beyond the end of the upper die I4 and the lateral dies I2, I3.
[0301] For imprinting the grooves, either lateral or upper, the installation comprises at least a rolling die I8, I9, I10 placed after the formwork I2, I3, I4 in the longitudinal direction X, there where the mould I7 extends, the rolling die I8, I9, I10 having continuous surface teeth I8T, I9T, I10T having axial direction of the die I8, I9, I10, the axis 8, 9, 10 of the die I8, I9, I10 being perpendicular to the longitudinal direction X, such that grooves 15, 26, 36 can be formed on the lateral 12, 22 or upper faces 14, 24 of the prefabricated floor elements 1, 2, 3.
[0302] According to an embodiment, shown in FIGS. 44 to 46, the installation comprises two rolling dies I8, I9 having vertical axis and arranged after each lateral die wall I2, I3, such that they allow to cast vertical continuous grooves in the prefabricated floor elements 2.
[0303] According to another embodiment, shown in FIGS. 41 to 43, the installation comprises a rolling die I10 having a horizontal axis and arranged after the upper wall I4, such that it allows to cast horizontal continuous grooves in the prefabricated floor elements 1.
[0304] A further embodiment is the result of combining the previous two embodiments. That is, an installation having two rolling dies having vertical axis and a rolling die having a horizontal axis, as shown in FIGS. 47 and 48; such that they can cast vertical and/or horizontal grooves in the prefabricated floor elements 1, 2, 3.
[0305] A particular embodiment of the installation IM3 depicted in FIGS. 47 and 48 is one that includes means, such as a clutch, to engage and disengage the rolling dies I2, I3, I4. Such a clutch enables installation I3 to effectively produce precast elements 1 or 2 or 3, depending on which of the rolling dies are engaged at the same time.
[0306] A particular embodiment of installations IM1, IM2, and IM3 is one that includes a device for counting the length of produced slab including grooves.
[0307] A particular embodiment of installations IM1, IM2, and IM3 is one that includes at list a device able to cause vibration to at least one of the rolling dies I2, I3, I4, while the mentioned rolling die rolls around its axis. This vibration while rotating enables a more appropriate compaction of the concrete when passing through the dies.
[0308] Formwork for Self-Consolidating Concrete Precasts
[0309] As shown in FIGS. 66 and 67, the invention also relates to another way to produce the inventive prefabricated floor elements 1, 2, 3 by using self-consolidating concrete.
[0310] FIG. 66 shows an installation IM11 comprising a formwork elongated in a longitudinal direction X, the formwork comprising a lower part I21 and a removable upper part I24 having teeth I24T perpendicular to the longitudinal direction X, such that grooves 15, 26, 36 can be formed on the upper faces 14, 24 of the prefabricated floor elements 1, 2, 3.
[0311] In this case, the removable upper part I24 is formed by a plurality of former structural profiles I241 perpendicular to the longitudinal direction X. The mentioned upper part I24 is removeable to allow for the demoulding of the precast member once it has hardened, but it typically stays stationary during the hardening process of the concrete.
[0312] The lower section L24 of the former structural profiles I24I defining a decreasing section that defines the section of the grooves 15, 26, 36, the upper section U24 of the former profiles I24I defining a constant section.
[0313] Therefore, to mold the floor elements 15, 26, 36 with self-consolidating concrete, the volume of the lower part of the mold must be filled up to the section change between the lower L24 and upper U24 section of the former profiles I24I.
[0314] The space G22 between each elongated former element I23 makes it easy to pour concrete, and avoids the formation of interior air bubbles, as the air can easily be evacuated by the multiple spaces.
[0315] The placing of the self-consolidating concrete may either be carried out once the upper part I22 is assembled to the rest of the installation Im11, or may the upper part I22 be put in place after the placing of concrete. In this second case, the upper part I22 must be placed right after placing the concrete, while this is still liquid, so that the elongated former elements can properly displace the liquid to form the grooves.
[0316] The upper part I24 further comprises joining profiles I24B having the longitudinal direction X and joined to an upper surface of the former profiles I24I, such that the former profiles I24I and the joining profiles I24B form a removable grid.
[0317] FIG. 67 shows an installation IM12 comprising a formwork elongated in a longitudinal direction X, the formwork in turn comprising a lower part I21, and a removable upper part I22 having teeth I22T perpendicular to the longitudinal direction X, such that grooves 15, 26, 36 can be formed on the upper faces 14, 24 of the prefabricated floor elements 1, 2, 3.
[0318] In the installation IM12, shown in FIG. 67, the upper part I22 has a lower perimeter equal to the shape of the superior grooves of precast floor elements 1, 3; and the upper part 122 comprises at least to ducts connecting the interior of the formwork to the interior. One of the ducts, used to inject liquid concrete in the formwork, and the other one to allow the evacuation of the air enclosed in the formwork, as it is pushed out by the liquid concrete.
[0319] In this text, the term comprises and its derivations (such as comprising, etc.) should not be understood in an excluding sense, that is, these terms should not be interpreted as excluding the possibility that what is described and defined may include further elements.
[0320] Thought the document one of the main features that characterizes the invention is the existence of continuous grooves. However one must understand that in the scope of this invention are also included continuous protrusions. I fact, grooves and protrusions are only two ways of referring to a same thing. One can understand that between each pair of grooves there is a protrusion or vice versa. Thus, defining groves is equivalent to indirectly defining protrusions.
[0321] The invention is obviously not limited to the specific embodiments described herein, but also encompasses any variations that may be considered by any person skilled in the art within the general scope of the invention as defined in the claims.
