Damage Mechanism Of Structures Research Articles

Experimental study of the mechanical properties and microscopic mechanism of carbonate rock subjected to high-temperature acid stimulation

To clarify the effect of acidification on the stress distribution around wells in deep carbonate reservoirs, it is necessary to study the changes in mechanical properties of carbonate rocks under different acid stimulation conditions. In this paper, a novel acid stimulation experiment is designed to investigate the mechanical properties of the carbonate rock through a self-built acid-rock reaction experimental system and triaxial rock mechanics apparatus. The changes in the core mechanical parameters with the acid stimulation time at different acid stimulation temperatures are obtained. Based on stress relaxation, the rheological properties of the core after acid stimulation are explored. The internal structural damage mechanism of the core after high-temperature acid stimulation is as analysed via by SEM. This research finds that the elastic modulus and compressive strength of the core exponentially decrease with increasing of acid stimulation time. The higher the acid stimulation temperature, the faster the core damage rate changes, and the earlier the damage amount tends to stabilize. The core has an obvious rheological mechanical property after acid stimulation. The stress relaxation amplitude exponentially increases with increasing strain during loading. Interestingly, when the acid stimulation temperature reaches 120 °C, a sudden stress drop occurs during stress relaxation. It is also found that the stress relaxation amplitude increases exponentially with increasing acid stimulation time under the same strain level. Moreover, a higher acid stimulation temperature results in greater stress relaxation under a constant acid stimulation time and strain. In addition, the core skeleton is destroyed through acid stimulation, and many complex damaged structures appear inside the core, which leads to a decrease in the core strength, which is the reason for the enhanced rheological characteristics of the rock after acid stimulation. These results can provide insights into the mechanical response mechanism of wellbore acidification.

Comparative analysis of blast load transfer and structural damage in multi-cabin structures during air and underwater explosions

This study presents comprehensive experimental and numerical findings regarding the impact of the fluid medium on blast load transfer and structural damage mechanisms in multi-cabin structures subjected to air and underwater explosions. The experiments demonstrated that the structure primarily underwent a comprehensive dynamic response during an air explosion. In contrast, underwater explosions induced severe localized damage, with fluid properties significantly influencing the shockwave intensity. The observed plastic deformation, shear tearing of the structure, and shock wave characteristics in the experiment were successfully predicted through numerical simulations. Additionally, the numerical simulation unveiled distinct mechanisms of pressure changes in the cabin, attributing air and underwater explosions to transmitted pressure waves and compression shocks of the outer plate, respectively. The high-intensity shock waves generated by underwater explosions and bubble loads sequentially impacted the structure, resulting in more pronounced structural damage compared to the weaker shock wave effect of an air explosion. This study provides valuable insights for comprehending and predicting the response of multi-cabin structures in diverse explosion scenarios.

Study on structural damage mechanisms and defence of rectangular closed-section simplified hull girders with thinner plates under near-field underwater explosions

Understanding the damage mechanisms of typical ship structures under fatal underwater explosion loads is crucial for developing effective defensive measures. To provide references for enhancing the survivability of ships, this paper conducts analyses of the damage mechanisms of simplified hull girders (SHGs) using a combination of experimental and simulation methods, and proposes targeted structural improvements. Initially, two types of thin-walled rectangular closed-section SHGs are subjected to near-field underwater explosion experiments. Corresponding simulation models are established, and the validity of the computational results is verified. The progressive damage processes of SHGs in hogging and sagging are examined from a structural perspective. Furthermore, the thin-walled plate deformation transfer processes are analyzed. Finally, based on the analyzed damage mechanisms, targeted defensive structures for overall damage are designed. The study results show that enhancing the anti-deformation capability of the upper and lower edges of the side plates can effectively improve the overall bending resistance of the SHG.

The impact of infill wall distribution on the mechanical behavior and failure patterns of multi-story RC frame structures: An acceleration–strain coupled testing approach

Historically, earthquakes have caused extensive damage to multi-story buildings, often leading to partial or total collapses. Nevertheless, these severely damaged structures rarely exhibit the "strong column–weak beam" failure pattern, and the performance of their vertical load-bearing components varies notably. Our study reveals that the uneven distribution of infill walls leads to divergent mechanical behaviors in columns located at different positions within the frame structure. To address this issue, an acceleration–strain coupled testing system was developed and implemented in a typical reinforced concrete (RC) frame structure of a veranda-style teaching building. This system, utilizing strong-motion seismographs for trigger acquisition, collected synchronized strain data from both columns adjacent to the veranda and those partially constrained by infill walls. Two sets of records were obtained, preliminarily confirming the internal force concentration due to the infill walls' constraints. Furthermore, the varied mechanical behaviors of components along two axes emerge as the primary factors causing significant structural damage and collapse. Based on these characteristic behaviors, quasi-static tests were conducted on frame columns, both unrestricted and partially restricted by infill walls. Results indicate that the constraining effect of the partial infill walls intensifies with deformation, markedly affecting column behavior. Notably, the load-bearing capacity, ductility, and ultimate displacement exhibited substantial differences between the two column types. The coexistence of these mechanically diverse components within the same structure leads to a sequence of failures, thereby altering the mechanisms of structural damage and collapse.

New perspectives on structural parameters of graphite materials revealed by micromechanics based on microstructural analysis

Graphite is used as a moderator and reflector in many nuclear reactors, where it is exposed to high temperatures, stress, radiation, and other harsh conditions. Under these conditions, graphite undergoes microstructural changes, the consequences of which can lead to deformation, cracking, and ultimately fracture. This research highlighted aims to investigate the microstructural based micromechanics of graphite materials and focus is on understanding the micromechanics based on microstructural degradation and changes in crystalline grain structure, their orientations, and boundaries in polycrystalline graphite for predicting structural damages in the graphite material. This study utilises analytical transmission electron microscopy to examine the nature of grain boundaries and extract important microstructural parameters. The crystallites and contained boundaries, including their orientations in a polycrystalline structure, all have the potential to influence the properties of the material. Under the harsh conditions of temperatures, radiation, and stress that graphite experiences in the reactor core, it is crucial to understand its microstructural behaviour and its influence on its properties. This research brings insight into the potential mechanisms of structural damage based on the nature of grain boundaries and crystalline orientations. The key investigations are the bending of crystallites along the interfaces, causing the division of coherently scattered domains into smaller crystallites. On analysing the traces across the crystallites, it was also observed that each crystallite was rotated in a similar direction. These crystallites bending is referred to as a micro-bending feature in graphite. This micro-bending deformation mode is less commonly observed in graphite, and the identification of these micro-mechanisms and their correlation with crystallite bending and rotation within polycrystalline structure provides insights into the deformation behaviour and potential degradation mechanisms in the graphite material.

Relationship between residential house damage and flood characteristics: A case study in the Teesta River Basin, Bangladesh

The flood damage function model is indispensable for flood damage assessment as it can provide useful information for establishing flood protection strategies. For the assessment of residential house damage in different areas, flood damage function models have been traditionally proposed considering only the depth–damage curve. However, flood duration and flood may also have an influence on flood damage. Conventionally, the damage rate was estimated based on information about monetary losses collected from local people or insurance payout databases. This research proposes a new methodology to establish a flood damage function model that considers flood depth, flood duration, and flood velocity. Field surveys were conducted in the Teesta River Basin of rural Bangladesh. For each house, a questionnaire survey was conducted to identify the flood information (flood depth, flood duration, and the qualitative representation of flood velocity), household structure information (area, plinth height, and ceiling height), structural damage mechanism, and the required amount of material and labor to repair the damage after each flood event. Finally, a flood damage function model including the impacts of house types and different flood parameters was established through multiple regression analysis. The consistency of the model was verified through the estimation of different statistical parameters. It can serve as a flood loss estimation model as it correlates flooding with various parameters, such as building materials and their damage mechanism.

Effect of buoyancy loads on the tsunami fragility of existing reinforced concrete frames including consideration of blow-out slabs

Currently available performance-based methodologies for assessing the fragility of structures subjected to tsunami neglect the effects of tsunami-induced vertical loads due to internal buoyancy. This paper adopts a generalized methodology for the performance assessment of structures that integrates the effects of buoyancy loads on interior slabs during a tsunami inundation. The methodology is applied in the fragility assessment of three case-study frames (low, mid and high-rise), representative of existing masonry-infilled reinforced concrete (RC) buildings typical of Mediterranean region. The paper shows the effect of modelling buoyancy loads on damage evolution and fragility curves associated with different structural damage mechanisms for existing RC frames with breakaway infill walls including consideration of blow-out slabs. The outcomes attest that buoyancy loads affect the damage assessment of buildings during a tsunami, especially in the case of mid and high-rise structures with blow-out slabs. The rate of occurrence of slabs uplift failure increases with the number of stories of the building, indicating the need to account for such damage mechanism when assessing the performance of structures. It is also found that buoyancy loads slightly affect the fragility curves associated to other structural damage mechanisms for existing RC buildings commonly monitored for fragility assessment.

Comparison of Vortex Cut and Vortex Ring Models for Toroidal Bubble Dynamics in Underwater Explosions

The jet impact from a collapsing bubble is an important mechanism of structural damage in underwater explosions and cavitation erosion. The Boundary Integral Method (BIM) is widely used to simulate nonspherical bubble dynamic behaviors due to its high accuracy and efficiency. However, conventional BIM cannot simulate toroidal bubble dynamics, as the flow field transforms from single-connected into double-connected. To overcome this problem, vortex cut and vortex ring models can be used to handle the discontinuous potential on the toroidal bubble surface. In this work, we compare these two models applied to toroidal bubble dynamics in a free field and near a rigid wall in terms of bubble profile, bubble gas pressure, and dynamic pressure induced by the bubble, etc. Our results show that the two models produce comparable outcomes with a sufficient number of nodes in each. In the axisymmetric case, the vortex cut model is more efficient than the vortex ring model. Moreover, we found that both models improve in self-consistency as the number of bubble surface elements (N) increases, with N=300 representing an optimal value. Our findings provide insights into the numerical study of toroidal bubble dynamics, which can enhance the selection and application of numerical models in research and engineering applications.

Numerical study of the interaction between an internal solitary wave and a submerged extended cylinder using OpenFOAM

To investigate the impacts of cylinder extended length, rotation angle and wave incidence angle on hydrodynamic characteristics, the numerical simulation of an internal solitary wave (ISW) interaction with a submerged extended cylinder is conducted by using OpenFOAM. The accordance between the experimental data and numerical simulation forces on the isolated cylinder shows that the OpenFOAM-based numerical model can deal with the ISW-submerged cylinder interaction. The distributions of forces, maximum dynamic pressure forces and flow field around the submerged extended cylinder are discussed to reveal the hydrodynamic characteristics of submerged cylinder under the ISW action. The horizontal forces on an extended cylinder are found to change from increasing to decreasing with the increase in extended length when the extended length is 2.5 times the cylinder diameter. The forces on the cylinder are sensitive to the change in the rotation angle. Both the horizontal loads and the evolution of the wave profile are easily affected by the change in incidence angle. The vortices shedding around the cylinder varies with the change of wave incidence angle. Investigation of the ISW and a submerged cylinder interactions can help to understand the mechanism of structural damage in internal wave ocean environment.

Establishment of flood damage function model for rural roads: A case study in the Teesta River basin, Bangladesh

Numerous studies have focused on the impact of flooding on road transportation conditions. However, a specific methodology for estimating direct damage by floods on roads considering flood and road characteristics is still missing. To bridge this gap, detailed field studies were conducted in rural Bangladesh's Teesta River Basin. The questionnaire was designed to collect information regarding flood characteristics (quantitative flood depth and qualitative flood velocity), road structure (length, width, and height above the ground), structural damage mechanism, and damaged part dimensions (length, width, and thickness) for each road segment. A flood damage function model, which considers the effects of flood factors (depth and velocity) and road characteristics (top surface material, width, and height from the ground), was created using multiple regression analysis. The consistency of this model has been examined by estimating statistical parameters, such as the Akaike information criterion, correlation coefficient, and variance inflation factor. The results showed that earth roads have suffered significant damage in contrast to Bituminous concrete (BC) roads. Less flood damage may result from a road segment that is wider but has a low height from the ground. This study can provide a straightforward model for estimating road damage for flood events in future studies.

Study on Dynamic Response Characteristics and Damage Mechanism of Tunnel Lining at Entrance of Shallow Bias Tunnel

The structural damage of the lining structure at the entrance of a tunnel is the most common instability problem. The instability problem may cause dynamic effects such as earthquakes and blasting. Based on the seismic damage data collected from previous major earthquakes at the entrance of shallow-buried tunnel, the shaking table test and numerical simulation are used to analyze dynamic response characteristics and damage evolution characteristics of the tunnel in the shallow-buried hole at 30°. The study revealed the stress characteristics of tunnel lining and the mechanism of structural damage under earthquake excitation. The research results show that the biased tunnel (30°) is susceptible to damage on the unsymmetrical loading side, the biased ground surface leads to acceleration, and high speed also significantly increases the effect. The biased side leg of the tunnel lining cross section is a location with a large internal force distribution. The biased tunnel has a relatively unfavorable internal force value distribution and a larger peak, and the peak at the larger bias side has the largest peak value. The skewback and spandrel portion of the biased tunnel lining load are more likely to be damaged.

Tendons exhibit greater resistance to tissue and molecular-level damage with increasing strain rate during cyclic fatigue

Musculoskeletal soft connective tissues are commonly injured due to repetitive use, but the evolution of mechanical damage to the tissue structure during repeated loading is poorly understood. We investigated the strain-rate dependence of mechanical denaturation of collagen as a form of structural microdamage accumulation during creep fatigue loading of rat tail tendon fascicles. We cycled tendons at three strain rates to the same maximum stress relative to their rate-dependent tensile strength. Collagen denaturation at distinct points during the fatigue process was measured by fluorescence quantification of collagen hybridizing peptide binding. The amount of collagen denaturation was significantly correlated with fascicle creep strain, independent of the cyclic strain rate, supporting our hypothesis that tissue level creep is caused by collagen triple-helix unfolding. Samples that were loaded faster experienced more creep strain and denaturation as a function of the number of loading cycles relative to failure. Although this increased damage capacity at faster rates may serve as a protective measure during high-rate loading events, it may also predispose these tissues to subsequent injury and indicate a mechanism of overuse injury development. These results build on evidence that molecular-level collagen denaturation is the fundamental mechanism of structural damage to tendons during tensile loading. Statement of significanceThis study is the first to investigate the accumulation of denatured collagen in tendons throughout fatigue loading when the maximum stress is scaled with the applied strain rate. The amount of denatured collagen was correlated with creep strain, independent of strain rate, but samples that were cycled faster withstood greater amounts of denaturation before failure. Differential accumulation of collagen damage between fast and slow repetitive loading has relevance toward understanding the prevalence of overuse musculoskeletal injuries following sudden changes in activity level. Since collagen is a ubiquitous biological structural component, the basic patterns and mechanisms of loading-induced collagen damage in connective tissues are relevant for understanding injury and disease in other tissues, including those from the cardiovascular and pulmonary systems.

A review on internal blast damage effects of multi-box type structures

The damage mechanisms of structures under internal blast are important for the prediction and evaluation of damage effects of conventional weapons and the design of anti-explosion structures of buildings and ships. The researches status and existing problems are discussed in this paper, based on the following four aspects as the internal explosion loads on structures, the plastic responses of structures to internal explosion loads, the damage modes of box-wall structures under internal explosion loads, and the damage modes and distribution of multi-box structures under internal explosion loads. With respect to an internal blast load, it is recognized that the blast model can be divided into dynamic high-pressure stage and quasi-static pressure stage. The former is formed by the initial shock wave and reflection wave while the latter is mainly composed of expansion of detonation gas and chemical energy released by explosion. In regard to the plastic response of the structure under the internal blast load, the studies have shown that quasi-static pressure plays an important role in the response process. With respect to the damage mode of the internal blast loaded structure, the damage mode is greatly affected by the pressure relief mode and pressure relief speed, studies on the damage modes of the beam and plate were introduced. As regards the damage mode and distribution of multi-box structures under the internal blast load, the internal explosion damage of the metal box structure of ships was mainly introduced. Most of the current researches focus on the damage features and there is rarely systematic understanding and analysis for the damagemechanisms. Through the review of the research on the damage and damage of the structures under the internal blast load, suggestions are provided for further researches on: (1) the models to describe the internal explosion loads on more complex structures and the corresponding damage effects; (2) the mechanisms of dynamic response of the box walls to internal blast load; (3) the coupling effect of multi-box structures with internal explosion waves and detonation products; (4) the methods to quickly and accurately predict the damage mode, damage range and damage degree of structures under internal explosion loads.

Geotechnical modelling of the climate change impact on world heritage properties in Alexandria, Egypt

Alexandria is one of the Mediterranean UNESCO World Heritage sites at risk from coastal flooding and erosion due to sea-level rise. The city’s position on the Mediterranean coast means it is especially vulnerable to rising sea levels. Alexandria is one of UNESCO sites in Egypt at risk from flooding. All the archaeological sites in the northern coast of Egypt are also said to be at risk from coastal erosion. The flood risk in Alexandria is expected to reach a tipping point by 2050. This research presents the numerical analysis of geotechnical and structural damage mechanism of Catacombs of Kom El-Shoqafa and El-Shatbi Necropolis; the sites have the lowest topography in Alexandria induced by the sea level rise and heavy rain due to the Climate Change, based on Finite Element PLAXIS Code. The purpose of the study was to investigate the behavior fully-saturated soft rock/ hard soil subjected to ground water intrusions. The main objective of this study is to very accurately record and analyze geotechnical problems and induced structural failure mechanisms that have been observed and accounted for in field, experimental and Numerical studies. The land area is also vulnerable to coastal flooding. It is widely expected that the numerical analysis of such geotechnical problems will contribute to the preservation of cultural heritage. The present research presents an attempt and experimental study to design a PLAXIS 2D FE model to simulate hard soil/hard rock problems, distortion and stress analysis of the complex structure of the catacombs. Plastic modeling or Mohr—Coulomb model was used in advanced soils during various stages of numerical analysis. Results are recorded and discussed regarding stress and volumetric behavior of soil/rocks. Groundwater infiltration into pores or fissures of rock and soil has a great influence on the engineering mechanical properties of rocks and soils.

PRELIMINARY OBSERVATIONS AFTER THE 2020 AEGEAN SEA EARTHQUAKE

The October 30, 2020 Aegean Sea Earthquake occurred with a magnitude of M6.6 and caused significant damages across the city of Izmir, Turkey. Specifically, this paper presents the preliminary observation results based on; ground motion properties, local site conditions, code-based design procedures, and the structural damage mechanisms. In order to achieve this purpose, critical spectral characteristic of strong ground motion records were evaluated in advance. Then, the variables given in code-based design results were investigated based on base shear to structural weight ratio. Local site effects were considered by comparing the spectral amplitudes obtained for different strong ground motions recorded from stations with different soil characteristics (i.e. the shear wave velocity (VS30) averaged over top 30m of the soil profile). Primary temporal distributions of recorded earthquake sequences followed by the mainshock were detailed and the directionality characteristics of the strong ground motion recorded after the mainshock were summarized. Moreover, observed damage patterns in buildings are discussed and possible reasons were identified in terms of critical structural properties. Preliminary results generally represent the effect of local soil characteristics on the amplification of spectral properties.

Investigating the relationship between erosion-induced structural damage and lining displacement parameters in shield tunnelling

This study investigated the relationship between erosion-induced structural damage and lining displacement parameters for shield tunnelling using a finite element approach, which properly simulated the interaction between the eroded soil and tunnel structure as well as the details of the segmental liners. The interaction between the bolt rod and reserved bolt hole was simulated by a surface-surface contact. The lining concrete and bolt materials were simulated by plastic constitutive models. The internal erosion process was qualitatively modelled by a strength-and-stiffness reduction method with a progressive flow boundary on the tunnel surface. The structural damage mechanism and its relationship with the lining displacement parameters were then clarified by conducting a series of parametric studies. It was found that the damage to the lining concrete and the number of yielded circumferential bolts could be properly related to the maximum and average vertical convergence rates of the liners, respectively, while the maximum internal force of the longitudinal bolts could be identified by the axial deflection angle of adjacent liners.

Cortical anatomy plasticity in cases of cervical spondylotic myelopathy associated with decompression surgery: A strobe-compliant study of structural magnetic resonance imaging.

Using voxel-based morphometry (VBM), we studied cortical gray matter volume changes in patients with cervical spondylotic myelopathy (CSM) before and after cervical cord surgical decompression. We then discussed the structural damage mechanisms and the neural plasticity mechanisms involved in postsurgical CSM.Forty-five presurgical CSM patients, 41 of the same group followed-up 6 months after decompression surgery and 45 normal controls (NC) matched for age, sex and level of education underwent high-resolution 3-dimensional T1-weighted scans by 3.0 T MR. Then, VBM measurements were compared and cortical gray matter volume alterations were assessed among pre- or postsurgical CSM patients and NC, as well as correlations with clinical indexes by Pearson correlation.Compared with NC, presurgical CSM patients showed reduced gray matter volume in the left caudate nucleus and the right thalamus. After 6 months, postsurgical CSM patients had lower gray matter volume in the bilateral cerebellar posterior lobes but had higher gray matter volume in the brain-stem than did presurgical CSM patients. Postsurgical CSM patients had significantly lower gray matter volume in the left caudate nucleus but greater regional gray matter volume in the right inferior temporal gyrus, the right middle orbitofrontal cortex (OFC) and the bilateral lingual gyrus / precuneus /posterior cingulate cortex than did NC. Abnormal areas gray volume in presurgical CSM and postsurgical CSM patients showed no significant correlation with clinical data (P > .05).Myelopathy in the cervical cord may cause chronic cerebral structural damage before and after the decompression stage, markedly in outlier brain regions involving motor execution/control, vision processing and the default mode network and in areas associated with brain compensatory plasticity to reverse downstream spinal cord compression and respond to spinal cord surgical decompression.

Experimental and Numerical Assessment on Seismic Performance of Earth Adobe Walls

Earth buildings are common types of structures in most rural areas in all developing countries. Catastrophic failure and destruction of these structures under seismic loads always result in loss of human lives and economic losses. Wall is an important load-bearing component of raw soil buildings. In this paper, a novel approach is proposed to improve the strength and ductility of adobe walls. Three types of analyses, material properties, mechanical properties, and dynamic properties, are carried out for the seismic performance assessment of the adobe walls. These performed studies include that, material properties of the earth cylinder block, mechanical properties of adobe walls under quasi-static loads, and dynamic performance of adobe walls excited by seismic waves. On investigation of material properties, eighteen cylindrical specimens with a diameter of 100 mm and a height of 110 mm were divided into three groups for compressive, tensile, and split pull strength tests, respectively. The results of the three groups of tests showed that the yield strength ratios of compressive, tensile, and shear strength were about 1:0.3:0.2. In order to study the performance of structural components, three 1/3 scale model raw soil walls with a dimension of 1,200 mm in width, 1,000 mm in height, and 310 mm in thickness were tested under cyclic loading. The average wall capacity of the wall obtained by the test was about 13.5 kN and the average displacement angle was about 1/135. The numerical simulation experiment is used to explore the mechanism of structural failure. A three-dimensional finite element model is established by choosing the material parameters based on the above test outcomes. The accuracy of the numerical simulation experiment is verified by simulation and comparison of the above quasi-static test results. Further, the collapse process of raw soil wall under a seismic wave is simulated for exploring the response and damage mechanism of structure. Based on those systematically analyzed, some useful suggested guidelines are provided for improving the seismic performance of raw soil buildings.

Seismic vulnerability of prefabricated reinforced concrete frame structure based on local outsource steel tube bolted column–column connection

In this paper, the seismic performance of a prefabricated frame structure with a local outsource steel tube bolted column–column connect is evaluated from the perspective of seismic vulnerability theory. Firstly, a simplified model of the prefabricated frame structure was constructed and validated by experiments. Then, a six-story prefabricated reinforced concrete frame structure (PRCS) and a cast-in-situ reinforced concrete frame structure (CRCS) were designed as examples to get the increment dynamic analysis (IDA) of the structure under 12 ground motions, and the two-parameter damage model was used as the structural requirement index. As a traditional structural requirement index-the maximum inter-storey drift angle cannot accurately describe the mechanism of structural damage. Therefore, two types of damage models are compared and analyzed. In addition, in order to evaluate the damage of frame structure effectively, a new damage index weighted combination method is proposed, and its feasibility is verified. Finally, the IDA curve and vulnerability curve with Kunnath two-parameter damage model and the maximum inter-story displacement angle as the requirement index are drawn. The results show that the two-parameter damage model is more accurate than the maximum inter-storey drift angle model in evaluating the seismic performance of the PRCS and CRCS. It shows that the maximum inter-story displacement angle model can overestimate the collapse resistance of the PRCS by 60.7% on average, and the collapse resistance of the CRCS by 75.67% on average. The seismic performance of the CRCS is better than that of the PRCS as the seismic intensity increases. Although the seismic performance of fabricated columns is similar to that of cast-in-place columns, there is still a certain gap in the seismic performance of frame structures.

Shaking Table Test of Seismic Response of Immersed Tunnels under the Influence of Multiple Factors

To explore the dynamic characteristics and influencing factors of immersed tunnels under the action of earthquakes, 5 groups of shaking table model tests were carried out. Three different site conditions (unsaturated sand site, homogeneous saturated sand site, and nonuniform site), structural stiffness, and seismic wave input direction were considered. By comparing the above influencing factors, the seismic response law affecting the immersed tunnels was obtained. The test results show that, under the action of horizontal earthquakes, the liquefaction of sand and the larger tunnel stiffness may influence the acceleration development of the soil layers; seismic wave input directions affect the excellent frequency and frequency range of the soil layers, and the liquefaction of sand and large structural stiffness change the shape of the Fourier spectrum curve of the soil layers; site conditions, structural stiffness, and seismic wave input direction have a significant effect on the internal forces of tunnels. Normally, the strain in the heterogeneous soil layer under the horizontal seismic wave input is the largest, and the peak strain of the upper side of the tunnel side wall and center column is larger than the lower part, while the mechanism of structural damage caused by vertical earthquakes is different.