Wenchuan Wave Research Articles

Full-scale shaking table tests of cross-laminated timber structures adopting dissipative angle brackets and hold-downs with soft-steel and rubber

Cross-laminated timber (CLT) has recently attracted significant interest in building timber or hybrid structures owing to the rapidly growing demand for low-carbon construction materials with excellent mechanical properties. To investigate the seismic performance of CLT structures adopting novel dissipative angle brackets and hold-downs with soft-steel and rubber (i.e., SRD-ABs and SRD-HDs), a series of shaking table tests were performed on two full-scale specimens, i.e., a benchmark specimen (Specimen Ⅰ) and a specimen with a multi-doorway at the ground (Specimen Ⅱ). Several representative ground motions, including the Turkey wave, El Centro wave, Wenchuan wave, and Shanghai artificial wave, were selected as excitations, whose peak acceleration increased gradually from 0.035 g to 0.80 g. The damage patterns of the structures were revealed, and the dynamic characteristics and responses were obtained and analyzed. The results show that the fundamental frequencies of Specimen Ⅰ and Specimen Ⅱ were 4.125 Hz and 3.625 Hz, respectively. The mode shapes of each specimen remained similar before tests with peak ground acceleration (PGA) of 0.51 g, with only a slight decrease of approximately 5 % in the fundamental frequency, indicating that the specimens only suffered minor damage because of the great energy-dissipating capacity of the SRD-ABs and SRD-HDs. After experiencing tests with PGA of 0.80 g, the specimen exhibited a maximum inter-story drift of 1/60 with a structural damping ratio of 13 %, and the damage was mainly exhibited at the SRD-ABs and SRD-HDs, which realized the performance objective of replaceability of dissipative connections and repairability of structures under the 9-degree rare earthquakes. Furthermore, non-linear numerical models were developed to duplicate the dynamic characteristics and responses of the test specimen, and the analytical results from the models show satisfactory agreement with the test results. Overall, the outcomes of this paper can provide valuable references for future research and applications of CLT structures with the SRD-ABs and SRD-HDs.

Model Test Study on Dynamic Response of Expressway Plastic-Reinforced Earth Embankment under Earthquake

Aiming at the seismic response of plastic geogrid-reinforced embankments, with Zhounan Expressway as the research engineering background, a self-designed seismic-rainfall coupled slope model test system was designed and used to produce 1 : 20 scale plastic geogrid-reinforced embankments. Moreover, the physical model of the unreinforced embankment under Hanshin wave, Wenchuan wave, Tianjin wave, etc. was also studied to carry out comparative analysis on seismic response and dynamic response on test model. The dynamic characteristics and dynamic response of the embankment model were tested from low to high seismic intensity; the changes of the embankment’s natural frequency, damping ratio, acceleration at the measuring point, and dynamic earth pressure were analyzed; and the main influencing factors and damage to the embankment seismic response feature were discussed herein. The test results showed that the initial natural frequency of the reinforced embankment was 42.4% higher than that of the unreinforced embankment, and its initial damping ratio reduced by 19.4%. The attenuation effect of the natural frequency and damping ratio of the reinforced embankment with the loading history was significantly lower than that of the unreinforced embankment. Embankment reinforcement exhibited a very good inhibitory effect on the PGA amplification effect of the embankment, and the inhibitory effect on the interior of the slope was more significant than that on the slope. Moreover, the type of seismic wave, the amplitude of the seismic wave, and the frequency of the seismic wave significantly influenced the PGA amplification effect of the embankment. The peak dynamic soil pressure of the unreinforced embankment at the same location was significantly greater than that of the reinforced embankment. The two embankment models showed significantly different antivibration damage performance. After the peak acceleration of 2 m s-2 was loaded, no cracks were seen on the surface of the embankment model. When the peak acceleration of 3 m s-2 was loaded, on the slopes of the two embankment models, smaller cracks were observed in the middle and upper parts of the face. When the peak acceleration of 4 m s-2 was loaded, the failure of the unreinforced embankment model was obvious. Large cracks on the top of the slope could reach 16 mm in width, and 27 mm settlement appeared at the top, and the slope was convex. The reinforced embankment model was only on the slope shoulder. Moreover, there were fine cracks on the top, and the slope top settlement was less than 5 mm. The research results provide theoretical support for preventing and controlling the road embankment vibration diseases and improving highway durability design.

Experimental study on acceleration response laws of shallow-buried bias tunnels with a small distance

Based on the similarity theory, a physical testing model with scale of 1:10 was designed and fabricated. The Wenchuan wave (WC-XZ), Darui artificial wave (DR-XZ) and Kobe wave (K-XZ) were adopted as excitation waves which was XZ directions (horizontal and vertical loading at the same time). A series of shaking table tests were carried out to study the effect of the types, directions and peaks acceleration of the seismic waves on the acceleration response laws of the shallow-buried bias tunnels with small distance. The results show that: (1) in the horizontal direction, the types of the seismic waves have a little effect on the acceleration response, but the law is opposite with Kobe wave being the most serious, followed by Darui artificial wave and Wenchuan wave in the vertical direction. (2) The existing slope has a significant effect on the acceleration response of the right hole which is different from that of the left hole. (3) The acceleration response of the tunnel in the vertical direction is more severe than that of the horizontal direction and the acceleration amplification factors in vertical direction are is generally 1.02-3.94 times that of the horizontal direction. (4) in the seismic design of tunnel, different seismic measures should be adopted in different directions. The results have a significant reference for the anti-seismic design of the tunnel.

Experimental study on seismic response of soilbags-built retaining wall

The seismic performance of soilbags-built retaining wall model was studied experimentally. A series of small-scale shaking table tests with the input of different amplitude sinusoidal waves and a large-scale shaking table test in a designed laminar shear box with the input of the Wenchuan earthquake wave were carried out on soilbags' retaining wall models. For comparison, the small-scale shaking table tests were also conducted on horizontally reinforced retaining wall models. The horizontal acceleration responses, the Fourier spectra, the dynamic earth pressure and the lateral displacements of soilbags' retaining wall models were investigated in shaking table tests. The results show that the seismic response of the soilbags' retaining wall is equivalent to or even slightly better than that of the horizontally reinforced retaining wall. The fundamental frequency and the Fourier spectral characteristics of the soilbags’ retaining wall are similar to those of backfill sands. The dynamic earth pressure of the wall model fluctuates almost synchronously with the input Wenchuan wave and no residual earth pressure is induced by the seismic loading. The permanent lateral displacements are small when subjected to multiple shakings, providing a proof that the retaining wall of soilbags has a good seismic performance.

Large‐Scale Shaking Table Test of Seismic Response Laws for a Shallow Double‐Arch Tunnel under Unsymmetrical Pressure with a Damping Layer

Based on the similarity theory, a large‐scale shaking table test of a shallow double‐arch tunnel under unsymmetrical pressure with a similarity ratio of 1 : 20 was designed and completed, and a foam concrete damping layer was set in the double‐arch tunnel. The acceleration response, strain response, and crack distribution of double‐arch tunnels under different intensities and different directions of the Wenchuan wave excitation were studied (WC‐X, WC‐Z, and WC‐XZ). The results showed that (1) the bias side (right hole) is greatly affected by the unevenness of the cover soil, and the horizontal acceleration response difference between the two tunnels is large and there is no symmetry. The incident direction of seismic waves has a great influence on the acceleration response of double‐arch tunnels. The amplification factor of WC‐Z is greater than that of WC‐X. (2) On the same horizontal plane, with the vertical centerline of the middle wall as the axis of symmetry, the vertical acceleration amplification factor also has a large difference between the arch foot and the shoulder, but the difference is relatively small at other points. (3) The dynamic strain increases with the increase of seismic intensity, and the tendency is similar under the three different seismic wave excitation directions. The lining is under tensile strain and compressive strain, the strain of the left hole is greater than the strain of the right hole, and severe stress concentration occurs at the top left of the mid partition. (4) The middle partition, shoulder, and vault of the left hole and the shoulder, vault, and foot of the right hole are weak parts of earthquake resistance. Therefore, special attention should be paid to the seismic design.

Study on seismic performance of steel frame with archaized-style under pseudo-dynamic loading

This paper presents an experimental study on a 1/2 scale steel frame with archaized-style under the pseudo-dynamic loading. Four seismic waves, including El Centro wave, Taft wave, Lanzhou wave and Wenchuan wave, were input during the test. The hysteresis characteristic, energy dissipation acceleration response, displacement response, strength, stiffness and strain were analyzed. Based on the experiment, the elastoplastic dynamic time-history analysis was carried out with the software ABAQUS. The stress distribution and failure mode were obtained. The results indicate that the steel frame with archaized-style was in elastic stage when the peak acceleration of input wave was no more than 400 gal. Under Wenchuan wave with peak acceleration of 620 gal, the steel frame enters into the elastoplastic stage, the maximum inter-story drift was 1/203 and the bearing capacity still tended to increase. During the loading process, Dou-Gong yielded first and played the role of the first seismic fortification line, and then beam ends and column bottom ends yielded in turn. The steel frame with archaized-style has good seismic performance and meets the seismic design requirement of Chinese code.

Shaking table test and numerical simulation for acceleration response laws of shallow-buried biased double-arch tunnel

In order to reveal the acceleration response law of shallow-buried bias double-arch tunnel under earthquake. The acceleration response of the shallow-buried biased double-arch tunnel under the action of Wenchuan wave was studied by the combination of shaking table test and numerical simulation. The effects of non-bias and bias on the acceleration response of shallow-buried biased double-arch tunnels were discussed. Research indicates: (1) Horizontal acceleration amplification factor of the left-hole (non-biased side) for the shallow-buried biased double-arch tunnel is V-shaped, and the right-hole (bias side) is ∩-shaped. The vertical acceleration amplification factor of the left-hole tends to increase continuously, and the right-hole shows a trend of decreasing first and then increasing continuously. (2) In the state of both the bias and the non-biased tunnel, the acceleration response in the vertical direction is stronger than that in the horizontal direction. (3) In the two states of bias and non-bias, the difference between the horizontal and vertical acceleration amplification factors of the double-arch tunnel is larger. It indicates that the excitation direction of the seismic wave has a great influence on the acceleration response of the double-arch tunnel. (4) Relatively biased double-arch tunnels, the regularity of non-biased double-arch tunnels is better, indicating that the bias voltage has a greater impact on double-arch tunnels.

Dynamic Response of Shallow-Buried Tunnels under Asymmetrical Pressure Distributions

Abstract Based on the similarity theory, two physical testing models (double-hole tunnel and single-hole tunnel) with a scale of 1:10 were designed and manufactured. A series of shaking table tests followed by numerical simulations was carried out to obtain the dynamic response characteristics of shallow-buried tunnels with asymmetrical pressure distributions. The similarities and differences in the dynamic response laws between double-hole tunnel and single-hole tunnel were studied. The effects of types of seismic wave (Wenchuan wave, Darui artificial wave, and Kobe wave), peaks acceleration excitation (0.1 g, 0.2 g, 0.4 g, and 0.6 g), excitation directions (horizontal and vertical directions), and excitation modes (unidirection and bidirection) on dynamic response laws of the tunnels were studied. The results show that the variation of acceleration multiplying factor (AMF) shows a nonlinear trend. The AMFs are different at different monitoring points. The type of seismic wave has a significant effect on the acceleration response, with Kobe wave being the most serious, followed by the Darui artificial wave and the Wenchuan wave. In bidirectional excitation, the AMFs are relatively larger than those of unidirectional excitation. A comparison between the numerical simulation and the shaking table tests in both acceleration time history and peaks acceleration shows that the results of the shaking table tests and numerical simulations are credible. The acceleration response of monitoring points near the existing slope is generally magnified. The residual strains are generated at the monitoring points. The variation trends of both tensile strain and compressive strain are opposite. The tensile strains are generally larger than the compressive strains. Many factors, such as the type of seismic wave, peaks of acceleration excitation, excitation direction, and excitation mode, have a significant influence on the dynamic strain response and acceleration response of the tunnels. The research results could promote the understanding of dynamic response characteristics of the tunnels.

Dynamic Responses of Bridge–Tunnel Overlapping Structure for High-Speed Railway Under Different Seismic Excitations

There are many bridges and tunnels been built overlapping or close to each other during railway constructions in west or south China recent years. For bridge–tunnel overlapping structures on high-speed railway, serious damage or even complete destruction could be caused when powerful earthquake occurred in complex topography or poor geological areas. However, there is still little research yet on this kind of complex system taking interactions of bridge–tunnel–rock into account, especially for seismic damage or dynamic response mechanism. For purposes of dynamic response analysis and reasonable anti-seismic measures for complex bridge–tunnel overlapping structures, large scale shaking table model tests have been carried out. In shaking table model test, EL-Centro wave (EL) and the Wenchuan wave (WC) were adopted as loading wave in X, Y, Z-direction (perpendicular to the tunnel axis, horizontal along the tunnel axis, and vertical). Test results demonstrated significant differences existing on dynamic responses or variation laws especially in different seismic excitation cases, and fateful consequences could be caused. It also indicated that several sensitive and fragile parts (e.g., the arch vault and arch foot at enlarged section of the tunnel, at the end of the beam and the top of the abutment inside the tunnel portal, and the soil above the tunnel roof etc.) should be strengthened or required special treatment for structural security or overall stability. Simultaneously, seismic excitation combination analysis is important for such overlapping structures in weak surrounding rocks or soils. And the influence caused by the tunnel longitudinal direction should not be ignored for seismic response analysis for such structures. Bidirectional or multi-directional seismic excitation method is proposed for the rationality and accuracy on seismic tests or anti-seismic analysis for same or similar structures.

The Large-Scale Shaking Table Model Test of the Shallow-Bias Tunnel with a Small Clear Distance

A physical shaking table test model of the shallow-bias tunnel with a small clear distance whose scale was 1:10 was performed to study the type, direction and acceleration peak of the seismic wave which have an immense influence on the dynamic response characteristics of the tunnel. In shaking table model test, the Wen Chuan wave (wc–xz), Da Rui wave (dr–xz) and Kobe wave (k–xz) were adopted as loading wave in x, z-direction (horizontal and vertical direction loading at the same time). The results show that under the action of seismic wave, the acceleration amplification factor of z-direction is generally larger than that of x-direction. Compared with the lining of the right hole, the acceleration amplification factor and variation trend of the lining of the left hole are highly different. The strain is less affected by the type of seismic wave, but that is greatly affected by acceleration peak. The tension strain increases with the increase of the acceleration peak of seismic wave, and is larger than the compression strain at each measuring point. The variation trend of tension strain is more intense than the compression strain.

Polygonal loop model for hysteretic behaviour of frame structures with recycled aggregate concrete

On the basis of shaking table tests on the recycled aggregate concrete (RAC) precast frame structure subjected to excitations of Wenchuan wave (WCW, 2008, N-S), El Centro wave (ELW, 1940, N-S) and Shanghai artificial wave (SHW), this study employed a new polygonal loop model (PLM) with its two core characteristics, that is, stiffness and strength degradation to describe the hysteretic behaviour of RAC frames. The implementation of the PLM model underwent different stages such as backbone curve, pivot points and unloading/reloading rules. The validation by shaking table tests on the precast RAC frame and application of the PLM to one cast-in-place RAC frame structure revealed that the hysteresis loops generated by the proposed PLM model not only traced the hysteretic trend but also fitted well with the tested hysteretic curves. Given these findings, it may be concluded that the new PLM model can be used to predict the seismic behaviour of RAC frame structures.

Characterization of fault zones by analysis of aftershock waveform data

Large property contrasts between materials in a fault zone and the surrounding rock are often produced by repeating earthquakes. Fault zones are usually characterized by fluid concentration, clay-rich fault gouge, increased porosity, and dilatant cracks. Thus, fault zones are thought to have re- duced seismic velocities than the surrounding rocks. In this article, we first investigated the synthetic waveforms at a linear array across a vertical fault zone by using 3D finite difference simulation. Syn- thetic waveforms show that when sources are close to, inside, or below the fault zone, both arrival times and waveforms of P- and S-waves vary systematically across the fault zone due to reflections and transmissions from boundaries of the low-velocity fault zone. The arrival-time patterns and waveform characteristics can be used to determine the fault zone structure. Then, we applied this method to the aftershock waveform data of the 1992 Landers M7.4 and the 2008 Wenchuan (汶川) M8.0 earthquakes. Landers waveform data reveal a low-velocity zone with a width of approximately 270-370 m, and P- and S-wave velocity reductions relative to the host rock of approximately 35%-60%; Wenchuan wave- form data suggest a low-velocity zone with a width of approximately 220-300 m, and P- and S-wave ve- locities drop relative to the host rock of approximately 55%.