Method for measuring the utilization of the load carrying capacity of the building structural element

Abstract

A method is shown for measuring the utilization of the load carrying capacity of a building structural element subject to variable action, including measurements of the rotation angles of cross-sections of this building structural element, wherein the rotation is caused by the variable action, wherein the rotation angles α1 and α2 of the cross-sections of the building structural element around the axis (Z) perpendicular to the longitudinal section of this building structural element are measured in two points (A) and (B) of this building structural element, located symmetrically relative to its transverse axis of symmetry, and subsequently the greater of the measured values of the angles α1 and α2 is used as the measure of the utilization of the load carrying capacity of the building structural element.

Claims

1. A method for measuring the utilization of the load carrying capacity of a structural element of a building subject to variable action, comprising measuring of rotation angles of cross-sections of the structural element, wherein the rotation is caused by said variable action, wherein the measuring of rotation angles comprises measuring a rotation angle α1 and a rotation angle α2 of the cross-sections of the structural element around an axis (Z) perpendicular to a longitudinal section of the structural element at two points (A, B) of the structural element located symmetrically relative to a transverse axis of symmetry, and subsequently using a greater of a measured value of the angle α1 and a measured value of the angle α2 as a measure of utilization of the load carrying capacity of the structural element.

2. The method according to claim 1, wherein the measuring of a rotation angle γ1 and a rotation angle γ2 of the structural element cross-sections around axes perpendicular to the cross-sections comprises also measuring at the two points (A, B) of the structural element, and subsequently using a value of angle γ1 and a value of angle γ2 as an indicator of stability loss of the structural element of the building.

3. The method according to claim 1, wherein the measuring of rotation angles is performed periodically.

4. The method according to claim 1, wherein the measuring of rotation angles is performed synchronously.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The method according to the invention is presented carried out in an embodiment in FIG. 1, which presents the load diagram of a single-span, frame-based building structural element and the measurement scheme of rotation angles, wherein Incl_1 and Incl_2 are inclinometers measuring the rotation angles α1 and α2 caused by the variable action and shown by the arrows 7 and 8, of the frame cross-sections around the axis Z perpendicular to its cross-section, in two points A and B of the frame, positioned symmetrically relative to its transverse axis of symmetry 6. In a preferable embodiment, the inclinometers Incl_1 and Incl_2 also measure the values of rotation angles γ1 and γ2 of the cross-sections of the frame around an axis perpendicular to these sections.

[0019] FIG. 2 is a simplified flow chart showing steps carried out according to an embodiment of the method as carried out for instance on the building of FIG. 1.

DETAILED DESCRIPTION

[0020] FIG. 1 presents schematically a sample building structural element in the form of a single-span frame. It will be evident to the skilled person that it is possible to use the method according to the invention to measure the utilization of the load carrying capacity of other types of structural elements, e.g. a beam, a truss, an arch or a part of an arch seated on vertical pillars or resting directly on the foundations.

[0021] As indicated above, FIG. 1 shows an example of symmetric attachment of two inclinometers Incl_1 and Incl_2 on a frame-based building structural element at the same distance d from the transverse axis of symmetry 6 of this structural element. The upper part of the drawing shows with arrows the variable load q(x) of the roof, e.g. due to snow, occurring over a part of the span with the length L1. The arrows 7 and 8 pointing downwards show the directions of rotation of the cross-sections of the structural element under a variable load in the region of attachment of the inclinometers Incl_1 and Incl_2. In the two indicated points A and B, the rotations have opposite directions. It is assumed that the values of rotation angles following the arrows 7 and 8 are greater than zero.

[0022] The points of attachment of the inclinometers Incl_1 and Incl_2 depend on the type of the structure, the type of the structural element and its span, indicated in FIG. 1 by the letter L (the spacing of piles). It is preferable that the inclinometers be fixed in points where the absolute values of the rotation angles α1 and α2 of the cross-sections caused by the variable action are as large as possible, preferably close to the maximum values.

[0023] Table 1 lists the results of simulation calculations for the framework structure system with sample defined parameters presented in FIG. 1, for the load q(x) changing from uniformly distributed across the entire length of the roof (L1=L, case 1 in Table 1) to located in ⅕ of the span (L1=0.2 L, case 9 in Table 1).

TABLE-US-00001 TABLE 1 Deflection values u in the middle of the span, the rotation angles α1, α2, the maximum stress σ.sub.max occurring in the element, the greater of the rotation angles α.sub.max and errors of measuring the utilization of the load carrying capacity for: deflection - δ1, the smaller of the rotation angles - δ2, the greater of the rotation angles - δ3, and the average value of the rotation angles - δ4, for the frame shown in FIG. 1 (L = 29.5 m and d = 11.25 m), for various load patterns - from one uniformly distributed across the entire length of the roof (L1 = L) to one located only in 1/5 of the span (L1 = 0.2 L). u α1 α2 σ.sub.max α.sub.max a.sub.av δ1* δ2** δ3*** δ4**** No. L1/L [mm] [°] [°] [MPa] [°] [°] [%] [%] [%] [%] a b c d e f g h i j k l 1 1.0 60.0 = 0.277 = 0.277 113.33 = 0.277 = 0.227 = 0 0 0 0 u.sub.0 α1.sub.0 σ.sub.max0 α.sub.max0 α.sub.av0 2 0.9 59.4 0.262 0.282 110.40 0.282 0.272 2 −3 4 1 3 0.8 56.8 0.213 0.293 113.82 0.293 0.253 −6 −31 5 −10 4 0.7 50.9 0.145 0.297 112.90 0.297 0.221 −17 −90 7 −25 5 0.6 41.6 0.078 0.285 101.51 0.285 0.182 −29 −218 13 −37 6 0.5 30.0 0.025 0.252 82.95 0.252 0.139 −46 −711 20 −46 7 0.4 18.4 −0.008 0.199 66.82 0.199 0.096 −92 2142 18 −71 8 0.3 9.1 −0.020 0.132 47.23 0.132 0.056 −175 677 13 −106 9 0.2 3.2 −0.016 0.064 26.13 0.064 0.024 −332 499 0 −166 *δ1 = [(u/u.sub.0 − σ.sub.max/σ.sub.max0)/(u/u.sub.0)]*100% **δ2 = [(α1/α1.sub.0 − σ.sub.max/σ.sub.max0)/(α1/α1.sub.0)]*100% ***δ3 = [(α.sub.max/α.sub.max0 − σ.sub.max/σ.sub.max0)/(α.sub.max/α.sub.max0)]*100% ****δ4 = [(α.sub.av/α.sub.av0 − σ.sub.max/σ.sub.max0)/(α.sub.av/α.sub.av0)]*100%

[0024] A reference value determining the utilization of the load carrying capacity of the presented frame is the maximum value of the stress σ.sub.max (column f in Table 1) in the frame (in any place).

[0025] An analysis of the calculation results presented in Table 1 shows that the values of the deflection u in middle of the span (column c in Table 1) and the smaller of the two measured rotation angles, in this case α1 (column d in Table 1), behave completely differently as a function of the change in load distribution (cases 2-9 in Table 1) from the maximum stress σ.sub.max (column f in Table 1) occurring in the frame. The use of these values (u and α1) as a measure of the utilization of the load carrying capacity of the structural element for a non-uniform load could result in very large errors (column i in Table 1 for the deflection u and column j in Table 1 for the angle α1). The method for measuring the utilization of the load carrying capacity based on measuring any of the two possible rotation angles, thus also including α1, is used—without any reservations—to monitor the building structure according to the prior art, i.e. the specification of FI118701B.

[0026] Another method, disclosed in PL230522, is based on the measurement of the average value of the rotation angles α.sub.av (column h in Table 1). The use of this value as the measure of the utilization of the load carrying capacity results in errors (column I in Table 1) reaching even −166% for a highly uneven load. An error value of less than zero additionally means that the current utilization of the load carrying capacity will be higher than the measured one (determined based on the measured values of the angle α.sub.av).

[0027] It is quite the opposite in the case of using the greater of the rotation angles α.sub.max (column g in Table 1), in this case α.sub.max=α2, of two cross-sections as a value representing the utilization of the load carrying capacity of the frame. The ratio of the value of the greater of the rotation angles α1 and α2 of the cross-sections α.sub.max (column g in Table 1) to the value of maximum stress σ.sub.max (column fin Table 1) is constant, with an error of no more than 20% for the presented frame (column k in Table 1), for changes in the unevenness of load within a wider range than what is observed in practice—from the uniformly distributed load across the entire length of the roof to one located only in ⅕ of the span. Such a value of the error is acceptable in the investigated application, especially since it is always higher than zero, which means that the current utilization of the load carrying capacity will be lower than the measured one (determined based on the measured value of the angle α.sub.max). Such a situation is safe; it poses no risk of overloading the structure by excessive utilization of its load carrying capacity.

[0028] In the case of using the deflection u, measured in the middle of the span of the frame (column c in Table 1), for determining the utilization of its load carrying capacity, the error of such determination (column h in Table 1) reaches a value of approx. −50% for a load located only on one roof surface (L1=0.5 L), or even on the order of −330% for a load located in ⅕ of the span. In addition, this error has a value lower than zero, which means that the current utilization of the load carrying capacity in this case would be higher than the measured one. Therefore, such a situation would be dangerous and it could pose a risk of overloading the structure.

[0029] The measurement of the utilization of the load carrying capacity of the building structural element (based on the measurements of the rotation angles α1 and α2) is possible when the building structural element is stable. The loss of stability means reaching the limit state of the utilization of the load carrying capacity regardless of the measured value of the utilization of the load carrying capacity. A loss of stability of the building structural element can be detected by means of optionally measured rotation angles γ1 and γ2, where a considerable change in one or both rotation angles can indeed mean a loss of stability.

[0030] Therefore, in structural systems of the single-bay frame type, the value of the greater of the rotation angles of cross-sections around the axis Z perpendicular to its cross-section, measured in two points of the structural system, situated symmetrically relative to the transverse axis of symmetry of the building structural element, caused by a variable action, represents the utilization of the load carrying capacity of the structure with sufficient accuracy for practice, within a scope of load changes which is real from a practical point of view. Similar error values are also obtained as a result of calculations for other types of structures, such as beams or trusses. In addition, the values of the rotation angles of cross-sections around axes perpendicular to these sections may serve the detection of a loss of stability of this system.

[0031] A flowchart is shown in FIG. 2 illustrating a method, carried out according to the foregoing description of the present invention, for measuring the utilization of the load carrying capacity of a structural element of a building subject to variable action. It includes a step of measuring of rotation angles of cross-sections of the structural element, wherein the rotation is caused by the aforementioned variable action, wherein the measuring of rotation angles includes measuring a rotation angle α1 and a rotation angle α2 of the cross-sections of the structural element around an axis (Z) perpendicular to a longitudinal section of the structural element at two points (A, B) of the structural element located symmetrically relative to a transverse axis of symmetry. To that end, tools such as inclinometers, light-based interrogators/sensors, or equivalent are employed to gather sensed signals having magnitudes indicative of the measured angles.

[0032] A processing step may then be carried out on the signals gathered during the measuring step to obtain usable measurement data. This may be done by a signal processor. In a subsequent step of using the measurement data, a greater of a measured value of the angle α1 and a measured value of the angle α2 is used as a measure of the utilization of the load carrying capacity of the structural element. This may include a comparison to a set signal value, a decision step, outputting a signal used to indicate the current situation, or the like.

[0033] The measuring of the rotation angle γ1 and the rotation angle γ2 of the structural element cross-sections around axes perpendicular to the cross-sections comprises also measuring at the two points (A, B) of the structural element, and subsequently using the value of angle γ1 and the value of angle γ2 as an indicator of stability loss of the structural element of the building.

[0034] It should be realized that the measuring of rotation angles may performed periodically as shown by the decision step after the step of using, thereby allowing for repeated steps of measuring, processing, and using again. The steps may be performed synchronously as well.