experimental research on end joint of steel-concrete composite truss.

by:ChangZeng     2020-06-29
Report on the final accounts of the parties, such as the parties, such.
Introduction and target steel-
Concrete composite truss is a new type of structure developed in recent years.
Since the strings at the top and bottom are all made of concrete used in various rail structures, the consumption of steel in the building has dropped sharply.
At the same time, the overall structure is stronger than the steel truss beam.
In addition, the steel structure is only applicable to network members, so the maintenance and construction costs are low.
In view of the above advantages, some research on the bridge type has been carried out and applied in engineering practice.
A series of combined truss bridges have been built in France (Tanis 2003), Germany (Reis 2011),Switzerland (Dauner et al. 1998)and Japan (Hirohisa et al. 2001; Koyama2003).
Composite joint is one of the important components of this convex beam structure.
Developing a new joint structure and understanding the behavior of the joint is the key.
The joint shall transfer the force properly and effectively between different materials.
From a practical point of view, there have been some experimental studies on effective joint alternatives, so various joints have been proposed and tested.
Udomworarat, etc. (2000; 2002)
The fatigue performance and ultimate strength of welded steel pipe joints are studied. Sakai et al. (2004)
Experimental study on ultimate strength and fatigue strength of concrete
Joints of truss beams. Toshio et al. (2004)
A new type of joint is proposed to weld the outer pipe to the steel plate outside the steel truss in the concrete slab.
Static loading test was carried out to verify the reinforcement performance. Kosuke et al. (2006)
Various connection structures are introduced and their features are illustrated.
In addition, some experiments and analysis are carried out on the design method of the new connection structure designed by the author. Sato etal. (2008)
Two joint structures using the perfobond shear head connector and the welding head studs head are proposed.
In order to clarify the stress transfer mechanism of the joint structure, the semi-dimensional loading test of the joint structure was carried out. Hino et al. (1985)
Bending test of steel
PSC beams and steel-
Reinforced concrete beams with three kinds of mechanical joints: ground bolts, bolts and bolts. Dunai (2004)
Investigate the behavior of the terminalplate-typesteel-to-
Concrete connected with bolts and bolts under combined compression shaft force and cyclic bending moment.
The concept of composite truss has been applied to large-
Railway bridges and other span bridges.
Experimental studies were conducted only (Kim et al. 2011; Takashi et al. 2002; Toshio et al. 2005; Xue et al. 2011)
On some combined truss bridges.
In 2009, steel-
Concrete composite truss used in Xi\'an
Pingliang railway.
In-depth research was conducted.
As shown in the figure, the top chord joint at the support of the composite truss bears the maximum unbalanced horizontal thrust from the concrete top string near the top chord1.
The combined Truss node consists of an oblique steel abdominal rod and a concrete string rod.
How to ensure the stress distribution between concrete and steel plate is still a key technical problem.
The characteristic of this plan is PBLconnectors (
Cruz e, Cruz 2004; Vianna etal. 2009)
Withstand shear and bending moments.
The preliminary application of this new composite truss structure in China requires a comprehensive understanding of its safety and applicability through experiments and numerical analysis.
Although some combined truss bridges have been constructed at present, there are few theoretical and experimental studies on such Bridge nodes.
The main drawback of these studies is that joint model tests have not yet been conducted.
The 1: 3 joint model was designed and tested at Central South University to evaluate the working performance, failure mode and ultimate bearing capacity of this joint. [
Figure 1 slightly][
Figure 2:2. Joint model 2. 1.
Introduction to the prototype joints of Xi\'an Houcun Bridge, Ma Wu Jingqiao and Taiyu bridge-
The Pingliang railway adopts 80 m steel with the same span.
As shown in the figure, the concrete composite truss1.
The main truss is a triangular truss with a height of 9 m, without any deformation.
The length of the joint is 10 m.
For the upper string, the rectangular section of reinforced concrete is used, which is 1.
The width is 1 m, 1. 2 m in height.
The bottom spine adopts a channel section with a beam height of 1.
5 m, beamend is 2. 0 m thick.
There are fully prestressed structures in the longitudinal direction and reinforced concrete structures in the transverse direction.
Rectangular steel box of 550x650 (mm)
Used for network components with wall thickness of 24mm. 2. 2.
Node model design the end joint point of the upper chord of the composite truss (Fig. 1)
Withstand unbalanced horizontal loads.
Due to the different mechanical behavior and deformation of concrete and steel bars, the mechanical behavior of joints becomes quite complicated.
In order to ensure that the joint has a reasonable bearing capacity and a safe and reliable structure, as shown in the figure, a structural scheme is proposed. 2.
The string wraps almost all the connecting plates on its expanded cross section.
Drill holes on the seam plate to ensure the bond strength between the concrete and the plate.
The reinforced reinforcement passes through the holes at the end of the connecting plate to form the PBL shear connector that bears the load transmitted from the string.
To withstand tensile and compression loads, the network members are welded at both ends of the connecting plate.
Experimental studies were conducted to better understand the ultimate bearing capacity and stiffness of the nodes, the stress and its distribution on the interface of steel bars and concrete, and the relationship between load and stress, load and strain, and the development trend of concrete cracks.
The bridge must bear the middle of the Chinese railway standard. live loading.
About the structure of single-
The maximum stress of the rail-assembled truss bridge is about 9000 kN.
Meet the requirements of the test equipment, two 1:3 joint models ZHJD-1and ZHJD-2 are produced.
The design load is 1000 kN.
The network members and joint plates of the sample are made of steel q345.
Made of concrete C50 and reinforced hrb3 35.
Figure 1 shows the detailed connection structure and its geometric dimensions. 3. 3.
Test process 3. 1.
For the purpose of loading, the test configuration and loading of the ground anchor slot and anti-force wall system in the civil engineering safety science laboratory of Central South University were adopted.
The connecting specimen is mounted on the loading base on one side of the reaction wall.
One end of the 5000 kN Jack rests against the reaction Wall and the other on the concrete string.
Apply horizontal force on the joint.
In order to ensure the axial movement of the sample during loading, vertical support and lateral pulley devices are provided at both ends of the string.
The loading device connecting the model is shown in the figure. 4.
The stacking method is used before the test to ensure the normal operation of all instruments.
Load control is used at the beginning of formal loading.
When the load is 0 ~ Between 2 000 kN, the load level is 400 kN.
When the load is kN ~ in 2000 ~ When between 3 000 kN, its load level is 200 kN.
When the load is increased to more than 3000 kN, the load level is 100 kN. 3. 2.
As shown in the figure, the strain and displacement data of the test items in this test were collected by strain gauges and dialgauge5.
A rectangular rose knot is provided on the concrete, connecting plate and network members of the string.
Other parts of the string are set with a horizontal strain gauge.
When the load is added to a load level that lasts 2 minutes, the static strain data acquisition instrument will start collecting the data.
The displacement measurement points and strain gauges of the two samples are arranged exactly the same. 4.
The mechanical properties of the material sample string in the test are made of concrete of c50.
China Railway turnout Bridge Company
Commissioned the production of steel structures using the samples of the steel. HRB335-
Grading force for making samples.
The mechanical properties of the materials are shown in Table 1. [
Figure 3 slightly][
Figure 4 slightly][
Figure 5 Slightly]5.
Test results 5. 1.
Description when 1600 kN is loaded on ZHJD-
1. uniform growth of strain and displacement.
The strain at each point is less than the strain of the material.
No concrete cracking and steel bar flexion were found.
In the process of increasing the load to kN in 2000, cracks first appeared in the concrete, mainly in the expanded cross-section, between the two web members, in the segmented angle of the compressed web members.
The crack develops along the direction of including the angle of 40, and has the axial direction of the string.
When the loading level increases, many new cracks appear on the concrete surface.
The position and development trend of the cracks are consistent.
When the load is increased to 2800 kN, cracks appear in the concrete at the corner of the section of the tensile network member, and the cracks are connected with the cracks on the concrete surface.
When the load is increased to 3200kN, the cracks on the concrete surface develop horizontally towards the load end.
Horizontal cracks develop quickly when the load is between 3600 kN and 3700 kN.
At the same time, there are two vertical cracks at the free end of the chord that run through the length of the chord.
Cracks on the concrete surface are shown in the figure6. [
Figure 6 slightly][
Figure 7 Slightly][
Figure 8:
When the load is less than 3300 kN, the measured point strain on the tensile and compression network members increases evenly, indicating that the network members are in the elastic stage.
Web members do not have any exceptions when the load keeps increasing.
But the strain at the measurement point increased quickly, indicating that the material began to yield.
When the load is increased to 3800 kN, the strain at the measurement point increases faster.
Expansion and bending are observed at the top of the compressed web member.
Load stops when compressed web members experience severe deformation.
There is no fault with the Tensile web member.
Local flexion of compressed network members as shown in the figure7. In ZHJD-
2, before the load is increased to 3200 kN, the measured point strain on the tensile and compression network members increases evenly, and the network members operate normally.
When the load is continuously increasing to 3500kN, neither network member fails, but the strain of the test point increases rapidly, indicating that the network member is not elasticplastic stage.
The cracks in the chords continue to develop, as shown in the figure8.
When the load increases to between 3500 kN and 3600kN, the strain at the measurement point increases dramatically.
Expansion and bending are found on the steel plate at the top of the compression network member.
The steel plate inside the lower part of the compression network member experienced tearing failure.
Severe deformation.
The loading station came to an end.
No macro fault was found on the tensileweb members.
As shown in the figure, the local flexion of the shaft member. 9.
From the above, the stiffness of the two joints is in the steel-
Specific interface.
No mutation was found in the stress distribution of steel
The concrete interface indicates the good mechanical properties of the surface and even the transfer of the load.
Experience of reinforced concrete (
Vertical and vertical).
The failure of the model is not controlled by the interface.
The joint has good shear stiffness and strength.
In composite truss nodes, it is feasible to connect steel bars and concrete with PBL shear bonds. 5. 2. Load-
Displacement graph
10 indicates the respective load-
Chord zjd-horizontal displacement curve at the free end1 and ZHJD-2. The load-
Horizontal displacement curve of ZHJD-
1 quite full, no obvious turning point.
Before the load increases to 3200 kN, the displacement increases as the load increases.
Although there is a crack at 2000 kN, there is no turning point in the curve.
At this time, the slope remains unchanged, and the impact of concrete cracking on the stiffness of the node is very small.
No stiffness drop occurred in the joint.
When the load increases to more than 3200 kN, the slope of the curve decreases gradually until it reaches the level.
The reason is that the web member material starts to yield at 3200 kN, causing serious deformation of the two joints first, and then the stiffness decreases.
The results show that the network components have a great influence on the mechanical properties of the nodes.
After the yield, the joint is seriously deformed and has good scalability, but has no brittle damage. The load-
ZHJD-horizontal displacement curve
2 similar to the development trend of ZHJD1.
But the curve of ZHJD
It is not full because it has an obvious turning point.
The final failure load is 3500 kN, which is lower than ZHJD-
But the displacement is large.
In general, the bearing capacity of both joints is greater than the design load of 1000 kN.
The node has a high safety factor and sufficient carrying capacity, which meets the design requirements and will be applied in engineering practice.
Table 2 shows the characteristic loads of the two joints obtained from their respective loads
The displacement curve is then compared with the design load.
The joint has sufficient bearing capacity to meet the design requirements.
Their cracking load is twice that of the design load. 5. 3. Load-
Judging from the strain curve of the joint failure mode, the two samples experienced the same failure, which proves that the analysis of the strain test results of the sample ZHJD-is correct2. Fig.
11 display load-
The axial strain measurement curve of the concrete test point.
When the concrete of the measuring point on one pillar is subjected to axial load, the strain at each measuring point is fully compressed.
Although these numbers are slightly different during the early loading phase, these differences are not significant at all.
No cracks can be seen here.
The strain experienced linear growth as the load increased.
There is no obvious turning point on the curve.
The measuring points in the 2nd column are located on the enlarged cross-section, and under the influence of whoseinfluence, the concrete is close to the tensile network member, and at the beginning of loading, the measuring points C8 and C9 experience tensile strain.
The strain increased linearly before the load increased to kN in 2000.
Under the influence of concrete pouring, the stiffness of the curve decreased slightly, but it still showed a non-linear growth.
When the load is increased to 3000 kN, a crack occurs at the measurement point.
When the slope of the curve drops sharply, the tensile strain increases very quickly.
The measured tensile strain of the Gauging point is much larger than the ultimate tensile strain of concrete.
The test points C5 and C5 are compressed at the top of the string.
It is far away from the joint and is not affected by concrete cracking.
The slope variation of their curves is less than that of C8.
When the tensile network members yield, the curve rotates sharply. [
Figure 9 omitted[
Figure 10 slightly]
The measuring point in the 3rd column is located at the center of the maximum cross-section.
At the beginning of loading, the strain is small.
As the load increases, the tensile stress of the concrete under bending-
The shear function exceeds the ultimate tensile strength.
At this time, cracks in concrete appear, and the strain increases rapidly.
When the load is increased to 3200 kN, under the influence of the yield of the network member, the curve rotates and the strain continues to grow.
In the subsequent loading phase, the strain of g12 suddenly dropped, indicating that the crack was out of the strain range.
The measurement points in column 4 are also on the expanded cross section.
Most of the load is assigned to the network members through the Node Board.
The strain at these points is smaller than the strain at the measurement point in the first three columns. From Fig.
The small strain increases linearly.
Under the influence of the stress concentration of the lower side of the compression network member, one of the test points experienced the tensile stress and the tensile stress developed rapidly.
When the crack exceeds this measurement point, the tensile stress increases rapidly. [
Figure 11 omitted]Fig.
12 display load-
Axial strain curves of tensile and compression network members.
At the beginning of loading, the load has a linear relationship with the strain.
The string rotates a bit when the joint is under load.
In addition to the axial load, the network members must also bear part of the additional torque, so the strain at each point is slightly different.
However, the difference is not large, indicating that the additional bending torque is small, and the network members mainly bear axial pulling and pressing loads.
When the load is 3300 kN, there is a turning point on the strain curve of the tension network member joint, indicating that the network member reaches its material yield strength.
The Joint began to yield, the level of the joint changed, and the bearing capacity of the Joint increased slowly.
At the same time, the strain increased rapidly.
Under the load of 3200 kN, the compressed network component is generated.
When the load stops, the strain drops quickly to almost zero.
The reason is that, in the subsequent loading phase, local flexion occurs in the finale members.
Its lower part bears the load and the steel plate at the corner of the part is torn.
The two test points are in the fault area. 5. 4.
According to the test process, the concrete failure modes of the two joints are almost the same: there are 40 diagonal cracks on the concrete surface, located at the section angle of the string.
The cracks on the string axis extend upwards until they become horizontal.
When the cracks under the seams extend down until they reach the compressed network component.
At the same time, because the network member is the section of the box girder, the stress concentration phenomenon will appear at the corner.
There are cracks on the concrete nearby.
They appear on concrete on compressed network members earlier than on stretched network members.
The cracks near the compressed network members are shortened and the development is slower.
Macro failure is not visible on stretched web members.
Local flexion occurs on compressed web members.
The steel plate near the concrete has expansion and depression, and the area is so large that it is almost equivalent to the height of the network members.
In addition, the steel plate at the bottom of the ZHJD compression web member-2 is torn.
There are three types of failure of the joint plate joint, I. e.
, Diagonal cracking of concrete on the surface of the joint, concrete cracking at the corner of the cross section of the web component, and bending failure of the compressed web component. 6.
The finite element analysis software ANSYS is used to analyze the joint.
Geometric dimensions of finite element models (FEM)
Same size as sample. Elastic-
The plastic housing element shell8 is used to simulate bracket and steel mesh members.
Solid elementSOLID65 is used to simulate concrete chords.
The composite plate and shear steel bars are simulated with solid unit SOLID45.
The 3-dimensional reinforcement unit LINK8 is used to simulate the reinforcement in concrete. Willam-
The concrete adopts the five-parameter failure criterion of Warnke.
Determine the material properties based on the most appropriate results.
Assume that all materials are ideal materials that meet Newton-Mises yield criteria
The Raphson iterative method is used to solve the problem.
At the same time, the non-material
Non-linear and geometric
Consider linear.
Because the test results show that the steel-to-
As shown in the figure, in the finite element analysis, the perfect connection between the concrete contact, the concrete and the joint plate is adopted13. [
Figure 12:[
Figure 13:Fig.
14 present Mises stress distribution (
Under the load of 3500kN)
Steel members.
There is obvious stress concentration inside the seam plate of the tension network member.
The maximum stress exceeds the yield stress of the material.
In addition to being buried in concrete, the remaining two network members have produced a maximum stress of 386. 2 MPa.
The calculation results are consistent with the test results. Fig.
15 Display measured and calculated load-
The free-end displacement curve of the string, from which the finite element analysis results are very consistent with the measurement results, except that the calculated yield point is a bit high.
When the load does not increase at the yield point, the joint stiffness decreases to zero.
Because it is related to the material\'s constructive relationship, a complete simulation is not achieved using the finite element analysis method. [
Figure 14 omitted][
Figure 15 omitted]
According to the test results and the finite element analysis results, the cracking load of the 1:3 model joint is 2000 kN, which is twice the design load.
The yield load is 3200 kN, which is 3.
Design twice the load.
The limit load is 3500 kN, 3.
5 times the design load.
High safety performance is ensured.
The finite element method developed is used to simulate the behavior of the joint. 7.
Based on the conclusion of Xi\'an Sanqiao-
Pingliang railway, a new structure--steel-
According to the construction features of concrete composite truss structure, the concrete composite truss structure is proposed.
Due to the complex interface load between steel and concrete, experimental study and finite element analysis of node plate nodes are carried out.
The following conclusions are drawn: 1.
According to the test results and the finite element analysis results, it is safe for the joint to bear the bridge load.
The shelf load is twice the design load.
The yield load is 3.
Design twice the load.
The limit load is 3.
5 times the design load.
High safety reserve and sufficient carrying capacity of Jointsenjoy.
The shelf load is 57% of the limit load and the yield load is 92% of the limit load.
The joint reaches the limit value soon after yielding, and the deformation is serious and has good scalability. 2.
Finite element calculation value of load-
The free-end horizontal displacement curve of the string coincides well with the measured value.
The finite element method is used to analyze and calculate the joint. 3.
There are three types of failure of the joint plate joint, I. e.
, Concrete diagonal cracking on the expansion cross section of the cable joint, concrete cracking at the cross section angle of the web component, and local flexion at the top and bottom of the compressed web component. 4.
The crack is mainly distributed on the surface of the string joint, and the angle between the axial direction of the string is 40 °.
The seam plate is buried in concrete and has good mechanical properties without any abnormalities.
Local flexion occurs on the extruded network members, resulting in the final failure of the joint. doi: 10. 3846/bjrbe. 2012.
40 admitted that the project received financial support from the Ministry of Science and Technology2008G007-C)
National Natural Science Foundation (50708112).
The research was supported by the first survey and design institute of China Railway.
The civil engineering safety science laboratory of Central South University provides test instruments and loading instruments.
Thanks to the professional review of the nameless serious reviewer.
The author wants to thank them.
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Received on November 29, 2011;
Zhou Lingyu was accepted on February 7, 2012 (1)
, *, Gui Chao he (2)(1)
School of Civil Engineering, Central South University, Shaoshan South Road, No.
22, Changsha 410075, China (2)
Changsha Institute of Design
No. 1 Xiangzhang Road Co. , Ltd.
254, Changsha 410014mails: (1)zhoulingyu@csu. edu. cn; (2)hgchao@csu. edu.
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