Computer structural model analysis and civil engineering testing technology

Abstract

In order to develop accurate and reasonable test theory, test method and corresponding structural design theory based on model test, Computer Structural Model and civil engineering detection technology are used. Firstly, through the study of theoretical knowledge of structural model, the design of test model is carried out. Secondly, the node and unit number of test model are given to carry out theoretical calculation of model. Thirdly, the strain of arch rib is observed through model test to simulate the stress status of real bridge, and other accessory members are also mechanically tested. Finally, the measured data of arch ribs, suspenders and other components are compared with those of the bridge site. The results show that the geometric size of the model is much smaller than that of the real structure. The model is relatively easy to make, easy to assemble and disassemble, material saving and cost saving. The test results can accurately reflect the actual mechanical characteristics of the structure.

Keywords

Structural model civil engineering detection technology finite element method calculation stress analysis

1. Introduction

With the continuous development of civil engineering construction, the form and function of structures are becoming more and more complex. People pay more and more attention to the quality and life of modern engineering. This work is providing a reliable technical guarantee for the extension of the service life of engineering structures and the further development of their benefits. Engineering structure detection has also been widely used in various fields [1].

However, in most cases in real life, it is impossible to use actual buildings as test objects to carry out load tests up to the failure stage, especially large, complex and special engineering structures [2]. Computer Structural Model is a model that reduces the size of the actual building according to a certain proportion and is used for testing. The results of Computer Structural Model test are based on the model theory to transform the combination of structural components. According to the requirements of Computer Structural Model analysis, the Computer Structural Model is designed and manufactured, and the corresponding loads are allocated. This process is called modelling process. Computer Structural Model test is based on a certain physical and geometric relationship, through the principle of model substitution to test and research, and the test results are applied to the original building of a test method [3].

2. Literature review

Computer Structural Model analysis and measurement data acquisition can be used to measure and evaluate buildings with entity structure. Old buildings will be damaged by natural and man-made reasons in the long-term use process, which will cause many unsafe factors to the structure of buildings. Therefore, the role of Computer Structural Model analysis in civil engineering detection is particularly important [4].

Ebrahimian et al. analyze accurately the actual detection technology, standard methods and methods of civil engineering, fully study the technical points of structural detection of civil engineering, reasonably analyze the key contents and links of civil engineering construction detection, put forward reasonable detection methods for actual construction technology, and strive to adopt reasonable technical detection standards. The method is analyzed to ensure its role in the actual overall construction of civil engineering [5].

According to the characteristics of civil engineering structure detection, Su et al. analyze the reliability of civil engineering structure detection, strive to use scientific and reasonable technical standards for civil engineering structure detection, and analyze the detection methods and methods in actual construction, so as to ensure that the overall construction of the building is carried out reasonably [6].

Zhao et al. carry out an accurate analysis of the methods and methods of the detection standard of the actual detection technology of civil engineering, fully study the technical points of the detection of the structure of civil engineering, reasonably analyze the key contents and links of the detection of civil engineering construction, put forward reasonable suggestions and solutions to the actual construction technology, and strive to adopt reasonable technical detection standards, and to carry out practical detection methods and methods. The method is analyzed to ensure the rationality of the actual integral construction function of civil engineering [7].

3. Methodology

In Computer Structural Model tests, stress, strain, displacement and load are the main measurement parameters. For stress, the strain value can be converted into the stress value by measuring the strain and the stress-strain relationship. For displacement and load, besides direct measurement, strain can also be measured and then converted into displacement or load.

At present, the commonly used strain measuring element which can basically meet the above requirements is the resistance strain measuring element, commonly known as strain gauge. The basic principle is to consolidate a resistance wire along the direction of strain measurement with the structure. When the structure is deformed, the resistance value of the resistance wire is changed by elongation or shortening. The variation of the measured resistance reflects the corresponding strain.

In general physics, the relationship between conductor resistance and deformation is discussed in detail. Usually the strain gauge is marked with a strain gauge coefficient, which combines the material section, line length and resistivity of the strain gauge resistance wire, and constitutes the following relationship.

$\displaystyle\Delta R=R\varepsilon F$ (1)

In the formula, $\Delta R$ is the variation value of strain gauge resistance ( $\Omega$ ). $R$ is the original value of strain gauge resistance. The strain value is measured by $e$ . $F$ is the strain gauge coefficient.

Wheatstone Bridge is the most widely used measurement method for strain acquisition. The bridge circuit in the resistance strain gauge is shown in Fig. 1.

It uses strain gauges or resistance elements as bridge arms. $R_{1}$ and $R_{2}$ can be used as strain gauges, or they are all in the form of strain gauges. The voltage $U$ is derived from Eqs (2)–(6).

$\displaystyle I_{1,2}=\frac{E}{R_{1}+R_{2}}$ (2) $\displaystyle I_{3,4}=\frac{E}{R_{3}+R_{4}}$ (3) $\displaystyle U_{A,B}=I_{1}R_{2}=\frac{ER_{1}}{R_{1}+R_{2}}$ (4) $\displaystyle U_{A,D}=I_{4}R_{4}=\frac{ER_{4}}{R_{3}+R_{4}}$ (5) $\displaystyle U=U_{A,B}-U_{A,D}=\frac{ER_{1}}{R_{1}+R_{2}}-\frac{ER_{4}}{R_{3}% +R_{4}}$ (6)

Table 1

Model geometric dimension table

	Prototype	Model design	Model adoption
Arch rib	1000 $\times$ 500	Square steel tube 60 $\times$ 30 $\times$ 2.5	Two square steel tubes 30 $\times$ 30 $\times$ 2
Suspender	13-7 $\phi$ 5	$\phi 6$	$\phi 6$
Tie beam	1400 $\times$ 1450 $\times$ 20	I 40 $\times$ 40 $\times$ 1.6	I 40 $\times$ 40 $\times$ 1.6
Beam	4000 $\times$ 4380 $\times$ 40	I 40 $\times$ 40 $\times$ 1.6	I 40 $\times$ 40 $\times$ 1.6
Bridge deck	967.68 m ${}^{2}$	4.8 m ${}^{2}$	4.8 m ${}^{2}$

Figure 1.

Whiston bridge line.

In order to ensure that the results of model test can more accurately reflect the structural performance of the real bridge, the test model should be designed and manufactured according to the similarity theory. The model should be similar to the prototype geometry as much as possible. The corresponding section stiffness of the model and the prototype should be as similar as possible. The boundary constraints of the model and the prototype should be same. In order to study the real performance of the structure, the material properties of the model must be the same as that of the original structure. However, considering that the actual working state of the bridge should be in the elastic range, many similar conditions can be relaxed without affecting the accuracy of the results.

The scale of the model is 1/15, in which the span of the model is 3.7 m, the height of the model is 0.74 m, the rise-span ratio is 1/5 and the bridge deck width is 1.52 m. The main similarity constants of the model are geometric similarity constant $C_{1}=$ 15.0, elastic modulus constant $C_{E}=$ 6.0, several load similarity constant $C_{P}=C_{E}C_{1}^{2}=$ 1350.0, and other physical similarity constants are functions of $C_{1}$ and $C_{E}$ .

The main geometric dimensions of the test model are listed in Table 1.

4. Results and discussion

4.1 Test model

The theoretical stress state under vehicle load is simulated, and the finite element model of spatial bar system is used to calculate by using structural analysis software. The spatial beam element is used to model the structure. Each natural junction of the structure is the calculation node, and the member between the two nodes is a unit. The two arch ribs are consolidated in three directions on one side and supported vertically. The suspender only bears tension and does not bear bending moment. The cable element only bears tension is adopted. The node number of the spatial finite element model is shown in Fig. 2 and the element number distribution is shown in Fig. 3.

Figure 2.

Node distribution of the model.

Figure 3.

Unit distribution of the model.

Under the most unfavorable vehicle load simulated, the arch rib mainly bears pressure and the maximum compressive stress is $-$ 1.95 Mpa. The longitudinal beam bears the maximum tensile stress of 1.00 MPa and the maximum compressive stress of $-$ 1.53 Mpa. The cross beam bears the maximum tensile stress of 0.63 MPa and the maximum compressive stress of $-$ 0.97 Mpa. The maximum tension of the suspender is 49 N. The maximum deflection locates at the junctions 30 and 31 in the midspan, and the value is $-$ 5.97 mm.

Table 2

Comparisons of different deflection values

Serial	Model computation	Model checking		Real bridge detection
number	value	Detection value	Detection error	Detection value	Similarity constant	Constant error
1	$-$ 4.99	$-$ 4.53	$-$ 9.22%	$-$ 65.68	13.16	$-$ 12.25%
2	$-$ 4.99	$-$ 4.51	$-$ 9.62%	$-$ 63.86	12.80	$-$ 14.68%
3	$-$ 5.43	$-$ 4.94	$-$ 9.02%	$-$ 65.52	12.07	$-$ 19.56%
4	$-$ 5.43	$-$ 4.90	$-$ 9.76%	$-$ 69.78	12.85	$-$ 14.33%
5	$-$ 5.97	$-$ 5.41	$-$ 9.38%	$-$ 74.91	12.55	$-$ 16.35%
6	$-$ 5.97	$-$ 5.39	$-$ 9.72%	$-$ 76.80	12.86	$-$ 14.24%
7	$-$ 5.75	$-$ 5.18	$-$ 9.91%	$-$ 74.47	12.95	$-$ 13.66%
8	$-$ 5.75	$-$ 5.18	$-$ 9.91%	$-$ 70.12	12.19	$-$ 18.70%
9	$-$ 2.72	$-$ 2.45	$-$ 9.93%	$-$ 32.11	11.81	$-$ 21.30%
10	$-$ 2.72	$-$ 2.45	$-$ 9.93%	$-$ 32.28	11.87	$-$ 20.88%
11	$-$ 3.17	$-$ 2.86	$-$ 9.78%	$-$ 41.28	13.02	$-$ 13.19%
12	$-$ 3.17	$-$ 2.87	$-$ 9.46%	$-$ 38.91	12.27	$-$ 18.17%
13	$-$ 2.56	$-$ 2.32	$-$ 9.38%	$-$ 30.96	12.09	$-$ 19.38%

Table 3

Comparison of different tensile stress values

Serial	Model computation	Model checking		Real bridge detection
number	value	Detection value	Detection error	Detection value	Similarity constant	Constant error
1	0.32	0.29	$-$ 9.38%	1.61	5.03	$-$ 16.15%
2	0.39	0.36	$-$ 7.69%	1.92	4.92	$-$ 17.95%
3	0.45	0.41	$-$ 8.89%	2.08	4.62	$-$ 22.96%
4	0.57	0.52	$-$ 8.77%	2.83	4.96	$-$ 17.25%
5	0.63	0.57	$-$ 9.52%	3.35	5.32	$-$ 11.38%
6	0.54	0.49	$-$ 9.26%	2.75	5.09	$-$ 15.12%
7	0.46	0.41	$-$ 10.87%	2.21	4.80	$-$ 19.93%
8	0.37	0.33	$-$ 10.81%	1.70	4.59	$-$ 23.42%
9	0.42	0.38	$-$ 9.52%	2.15	5.12	$-$ 14.68%
10	0.42	0.38	$-$ 9.52%	2.24	5.33	$-$ 11.11%
11	1.00	0.90	$-$ 10.00%	5.11	5.11	$-$ 14.83%
12	1.00	0.91	$-$ 9.00%	4.58	4.58	$-$ 23.67%
13	0.48	0.44	$-$ 8.33%	2.50	5.21	$-$ 13.19%
14	0.48	0.44	$-$ 8.33%	2.42	5.04	$-$ 15.97%
15	$-$ 0.35	$-$ 0.32	$-$ 8.57%	$-$ 1.64	4.69	$-$ 21.90%
16	$-$ 0.35	$-$ 0.32	$-$ 8.57%	$-$ 1.85	4.29	$-$ 11.90%
17	$-$ 0.46	$-$ 0.41	$-$ 10.87%	$-$ 2.11	4.59	$-$ 23.55%
18	$-$ 0.46	$-$ 0.42	$-$ 8.70%	$-$ 2.37	5.15	$-$ 14.13%
19	$-$ 0.37	$-$ 0.33	$-$ 10.81%	$-$ 1.86	5.03	$-$ 16.22%
20	$-$ 0.37	$-$ 0.33	$-$ 10.81%	$-$ 1.80	4.86	$-$ 18.92%
21	0.57	0.52	$-$ 8.77%	2.77	4.86	$-$ 19.01%
22	0.57	0.52	$-$ 8.77%	2.65	4.65	$-$ 22.51%
23	0.66	0.60	$-$ 9.09%	3.13	4.74	$-$ 20.96%
24	0.66	0.60	$-$ 9.09%	3.56	5.39	$-$ 10.10%

Table 4

Comparisons of different compressive stress values

Serial	Model computation	Model checking		Real bridge detection
number	value	Model checking	Detection error	Model checking	Similarity constant	Constant error
1	$-$ 0.57	$-$ 0.51	$-$ 10.53%	$-$ 2.60	4.56	$-$ 23.98%
2	$-$ 0.65	$-$ 0.59	$-$ 9.23%	$-$ 2.96	4.55	$-$ 24.10%
3	$-$ 0.74	$-$ 0.68	$-$ 8.11%	$-$ 3.66	4.95	$-$ 17.57%
4	$-$ 0.85	$-$ 0.77	$-$ 9.41%	$-$ 4.52	5.32	$-$ 11.37%
5	$-$ 0.97	$-$ 0.88	$-$ 9.28%	$-$ 5.25	5.41	$-$ 9.79%
6	$-$ 0.79	$-$ 0.72	$-$ 8.86%	$-$ 3.96	5.01	$-$ 16.46%
7	$-$ 0.70	$-$ 0.63	$-$ 10.00%	$-$ 3.74	5.34	$-$ 10.95%
8	$-$ 0.63	$-$ 0.58	$-$ 7.94%	$-$ 3.06	4.86	$-$ 19.05%
9	$-$ 0.98	$-$ 0.88	$-$ 10.20%	$-$ 4.68	4.78	$-$ 20.41%
10	$-$ 0.98	$-$ 0.88	$-$ 10.20%	$-$ 5.12	5.22	$-$ 12.93%
11	$-$ 1.53	$-$ 1.39	$-$ 9.15%	$-$ 8.03	5.25	$-$ 12.53%
12	$-$ 1.53	$-$ 1.39	$-$ 9.15%	$-$ 8.24	5.39	$-$ 10.24%
13	$-$ 1.11	$-$ 1.01	$-$ 9.01%	$-$ 5.44	4.90	$-$ 18.32%
14	$-$ 1.11	$-$ 1.01	$-$ 9.01%	$-$ 5.78	5.21	$-$ 13.21%
15	$-$ 1.68	$-$ 1.53	$-$ 8.93%	$-$ 8.69	5.17	$-$ 13.79%
16	$-$ 1.68	$-$ 1.53	$-$ 8.93%	$-$ 8.73	5.20	$-$ 13.39%
17	$-$ 1.95	$-$ 1.77	$-$ 9.23%	$-$ 10.46	5.36	$-$ 10.60%
18	$-$ 1.95	$-$ 1.76	$-$ 9.74%	$-$ 10.49	5.38	$-$ 10.34%
19	$-$ 1.86	$-$ 1.69	$-$ 9.14%	$-$ 8.91	4.79	$-$ 20.16%
20	$-$ 1.86	$-$ 1.68	$-$ 9.68%	$-$ 9.33	5.02	$-$ 16.40%
21	$-$ 1.41	$-$ 1.28	$-$ 9.22%	$-$ 6.58	4.67	$-$ 22.22%
22	$-$ 1.41	$-$ 1.28	$-$ 9.22%	$-$ 6.77	4.80	$-$ 19.98%
23	$-$ 1.71	$-$ 1.56	$-$ 8.77%	$-$ 0.70	5.09	$-$ 15.20%
24	$-$ 1.71	$-$ 1.55	$-$ 9.26%	$-$ 8.01	4.68	$-$ 21.93%

Table 5

Comparison of tension values of different suspenders

Serial	Model computation	Model checking		Real bridge detection
number	value	Model checking	Detection error	Model checking	Similarity constant	Constant error
1	0.43	0.45	$-$ 4.63%	570.54	1317.65	$-$ 2.40%
2	0.43	0.48	$-$ 9.22%	604.26	1395.52	3.37%
3	0.46	0.49	$-$ 7.32%	632.93	1388.01	2.82%
4	0.46	0.46	$-$ 1.72%	623.87	1368.13	1.34%
5	0.48	0.50	$-$ 3.02%	644.55	1340.02	$-$ 0.74%
6	0.48	0.49	$-$ 1.43%	671.86	1396.79	3.47%
7	0.49	0.54	$-$ 9.74%	646.19	1316.07	$-$ 2.51%
8	0.49	0.55	$-$ 10.40%	678.62	1382.12	$-$ 2.38%
9	0.48	0.49	$-$ 2.46%	630.05	1323.64	$-$ 1.95%
10	0.48	0.51	$-$ 6.48%	647.17	1359.60	0.71%
11	0.43	0.47	$-$ 8.76%	582.36	1363.83	1.02%
12	0.43	0.51	$-$ 15.45%	566.88	1327.59	$-$ 1.66%
13	0.44	0.46	$-$ 3.74%	569.66	1300.58	$-$ 3.66%
14	0.44	0.45	$-$ 3.67%	594.93	1358.28	0.62%
15	0.45	0.46	$-$ 3.88%	592.22	1327.84	$-$ 1.64%
16	0.45	0.45	$-$ 0.89%	601.51	1348.67	$-$ 0.10%
17	0.44	0.46	$-$ 4.34%	573.80	1301.13	$-$ 3.62%
18	0.44	0.46	$-$ 4.13%	586.06	1328.93	$-$ 1.56%
19	0.44	0.47	$-$ 4.73%	577.95	1304.63	$-$ 3.36%
20	0.44	0.47	$-$ 4.94%	596.73	1347.03	$-$ 0.22%
21	0.47	0.49	$-$ 3.29%	619.84	1316.01	$-$ 2.52%
22	0.47	0.47	$-$ 0.42%	653.38	1387.22	2.76%
23	0.48	0.51	$-$ 5.50%	671.02	1395.06	3.34%
24	0.48	0.50	$-$ 3.61%	657.84	1367.65	1.31%

4.2 Model test

According to the purpose of model test and the structural stress characteristics of tied arch bridge, the main test contents are suspender tension, main arch rib, longitudinal beam stress and beam deflection.

The stress measurement of arch rib and longitudinal beam is based on resistance strain gauge, which measures the strain at the testing point and calculates the elastic modulus of the material. The tension force of the suspender is calculated after calculating the stress, and then calculates the area of the suspender section. The strain gauge used in the model test is BE120-1AA, and its size is 3.6 $\times$ 2.6 mm ${}^{2}$ .

The deflection of the beam can be read directly by BEM-1 electromechanical percentile meter or by resistance strain gauge.

The layout of measuring points includes 6 arch ribs that are mainly located in the mid-span and near both sides. Eight crossbeams and 6 longitudinal beams are located near the mid-span. Each hanger is a measuring point, and the total is 24. There are also 13 deflection measuring points, including the wind brace intersection point.

4.3 Actual detection

The testing equipment used in the field is slightly different from that in the laboratory, but the principle is exactly the same. There are two main differences.

The method of measuring the deflection of the beam is to use the level to observe the change of the scale on the beam manually. The main reason is that there is no relatively static control point near the real bridge and the percentile meter cannot be fixed. The observation instrument is DS-1 precise level with a reading error of 2% mm. A stainless-steel ruler with a scale spacing of 0.5 mm is set at the lower edge of the beam body, and the error is less than 3% mm. The distance between the station and the observation point is between 20 and 25 m. Without considering the accidental error, the detection accuracy should be higher than 5% mm.

4.4 Data analysis

By comparing the actual bridge test data with the model test data and theoretical calculation value of the simulated load, the difference of the results of different methods in this group of tests can be understood.

Table 2 is a comparison of deflection data. The theoretical similarity constant of the deflection is 15.00, and the similarity constant and its error are given according to the measured value of the real bridge in the table. At the same time, the error of model detection and model calculation is also given.

From the table, it can be seen that the model detection values are less than the model theoretical calculation values, and the error is about 9%. The similarity constant of deflection is 12–13, and the error is about 15%.

Tables 3 and 4 are the comparison of tension and compression stress data. Similarly, the theoretical similarity constant of stress is 6.00, and the similarity constant and its errors are given according to the measured values of real bridges. At the same time, the errors of model detection and model calculation are also given.

It can be seen from the table that the measured values of the tensile stress model are less than the theoretical values of the model, and the error is about 10%. The error of stress similarity constant is large, which is between 10% and 20%. The large error may be due to the randomness of concrete strain detection.

Table 5 is a comparison of suspender tension data. The theoretical similarity constant of tension is 1350.00 based on the calculated value of the model. The similarity constant and its errors are given according to the measured value of the real bridge in the table, and the errors of the model detection and model calculation are also given. The table shows that the data of suspenders are ideal.

5. Conclusion

The model used in the Computer Structural Model test is a representative of the real structure duplicated according to a certain similarity relationship. It has all or main characteristics of the real structure. As long as the designed model satisfies the similar conditions, the data and results obtained from the model test can be directly inferred to the corresponding real structure. Compared with the real structure test, the Computer Structural Model test has the advantages of good economy, strong pertinence and accurate data.

References

Khan

M.I.

Mourad

S.M.

and Zahid

W.M.

, Developing and qualifying civil engineering programs for ABET accreditation, Journal of King Saud University – Engineering Sciences28(1) (2016), 1–11.

António

Casas

J.R.

and Sergi

, A review of distributed optical fiber sensors for civil engineering applications, Sensors16(5) (2016), 748.

Rana

Subramani

and Fangueiro

et al., A review on smart self-sensing composite materials for civil engineering applications, Aims Materials Science3(2) (2016), 357–379.

Ghosh

Rajesh

and Chand

J.S.

, Linear and nonlinear elastic analysis of closely spaced strip foundations using Pasternak model, Frontiers of Structural & Civil Engineering11(2) (2017), 1–16.

Ebrahimian

Astroza

and Conte

J.P.

et al., Nonlinear finite element model updating for damage identification of civil structures using batch Bayesian estimation, Mechanical Systems & Signal Processing84 (2017), 194–222.

Peng

and Hu

, A gaussian process-based dynamic surrogate model for complex engineering structural reliability analysis, Structural Safety68 (2017), 97–109.

Zhao

and Qiuyun

L.I.

, A review on measurement technology for structural testing in civil engineering, Journal of Xian University of Architecture & Technology49(1) (2017), 48–55.