scholarly journals Experimental study of the progressive collapse mechanism of excavations retained by cantilever piles

2017 ◽  
Vol 54 (4) ◽  
pp. 574-587 ◽  
Author(s):  
X.S. Cheng ◽  
G. Zheng ◽  
Y. Diao ◽  
T.M. Huang ◽  
C.H. Deng ◽  
...  
Keyword(s):  
Load Transfer ◽  
Progressive Collapse ◽  
Maximum Load ◽  
Influential Factors ◽  
Collapse Mechanism ◽  
Sudden Increase ◽  
Bending Moments ◽  
Transfer Coefficients ◽  
Collapse Mechanisms ◽  
Peak Increase

An increasing number of catastrophic progressive collapses of deep excavations have occurred throughout the world. However, the research on progressive collapse mechanisms is limited. In this paper, two categories of model tests were conducted to investigate the mechanism of partial collapse (sudden failures of certain retaining piles) and progressive collapse. The model test results show that partial collapse can cause a sudden increase in the bending moments of adjacent piles via an arching effect. The load-transfer coefficients are defined to be equal to the peak increase ratios of the maximum bending moments in adjacent piles (peak moments caused by collapse over the values before the collapse). When the maximum load-transfer coefficient is larger than the bearing capacity safety factor of the piles, the partial failure will lead to progressive collapse. The influential factors of the progressive collapse mechanism, such as the partial collapse extent, excavation depth, and capping beam, were also investigated. During progressive collapse, the previous failed pile could cause new stress arching; simultaneously, the soil behind certain nearest intact piles could become loosened and destroy the arch springing of the stress arching, causing the progressive collapse to cease gradually.

Experimental study on the progressive collapse mechanism in the braced and tied-back retaining systems of deep excavations

2020 ◽  
Author(s):  
Gang Zheng ◽  
Yawei Lei ◽  
Xuesong Cheng ◽  
Xiyuan Li ◽  
Ruozhan Wang
Keyword(s):  
Large Scale ◽  
Large Deformations ◽  
Load Transfer ◽  
Progressive Failure ◽  
Progressive Collapse ◽  
Collapse Mechanism ◽  
Bending Moments ◽  
Failure Path ◽  
Transfer Mechanisms ◽  
Very High

Collapses of braced or tied-back excavations have frequently occurred. However, the influence of the failure of some retaining structure members on the overall safety performance of a retaining system has not been studied. Model tests of failures of retaining piles, struts or anchors were conducted in this study, and the load transfer mechanisms underlying these conditions were analysed. When failures or large deformations occurred in certain piles, the increasing ratios of the bending moments in adjacent piles were much larger in the braced retaining system than in the cantilever system and more easily triggered progressive failure. When the strut elevation was lower or the excavation depth was greater, the degree of influence and range of pile failures became larger. When certain struts/anchors failed, their loads transferred to a few adjacent struts/anchors, possibly leading to further strut/anchor failure. The influence mechanisms of strut or anchor failure on piles were different from those of pile failure. As the number of failed struts or anchors increases, the bending moments of the piles in the failure zone first decrease and then increase to very high values. Therefore, the progressive failure path extends from struts/anchors to piles and will lead to large-scale collapse.

scholarly journals Research Status on the Collapse Mechanism and Prevention Measures of Mega Composite Structural Systems

2018 ◽  
Vol 175 ◽  
pp. 04008
Author(s):  
Wei Zhang
Keyword(s):  
Composite Structures ◽  
Failure Modes ◽  
Progressive Collapse ◽  
Structural Systems ◽  
Collapse Mechanism ◽  
Research Status ◽  
High Rise ◽  
Collapse Mechanisms ◽  
Verification Methods ◽  
Study Results

Mega composite structural system presents wide application prospects in high-rise and super high-rise buildings. However, research concerning the important issues of the seismic behavior, collapse mechanism, and prevention from progressive collapse for such new structural systems under severe earthquakes is quite limited. This paper will summarize the current research status, followed by the discussions on the collapse and prevention mechanisms of high-rise and super high-rise mega composite structural systems under severe earthquakes, the theoretical basis on progressive collapse mechanisms, numerical simulation techniques, and test methods. The failure modes of high-rise mega composite structures were studied firstly, followed by the collapse mechanisms and the associated criteria and indices. In addition, a new numerical technique for simulating the non-linear structural collapses considering large deformations will be presented, along with the relevant test results. This study shows that analysis method, damage accumulation model, failure criteria, appropriate preventive measures, and improved collapse experimental verification methods are all important seismic design considerations for high-rise and super high-rise mega composite structures. Based on the study results, recommendations for collapse and prevention mechanisms of high-rise buildings are proposed.

scholarly journals Analytical Evaluation of MCE Collapse Performance of Seismically Base Isolated Buildings Located at Low-to-Moderate Seismicity Regions

2020 ◽  
Vol 10 (24) ◽  
pp. 9150
Author(s):  
Hyung-Joon Kim ◽  
Dong-Hyeon Shin
Keyword(s):  
Base Isolation ◽  
Numerical Models ◽  
Influential Factors ◽  
Collapse Mechanism ◽  
Total System ◽  
Practical Applications ◽  
Seismic Design Code ◽  
Moderate Seismicity ◽  
Design Requirements ◽  
Isolation Systems

The promising seismic response emerged by the concept of base isolation leads to increasing practical applications into buildings located at low-to-moderate seismicity regions. However, it is questionable that their collapse capacities can be ensured with reasonable reliability, although they would be designed according to a current seismic design code. This paper aims to investigate the collapse capacities of isolated buildings governed by the prescribed design criteria on the displacement and strength capacities of the employed isolation systems. In order to evaluate their collapse capacity under maximum considered earthquakes (MCEs), simplified numerical models are constructed for a larger number of nonlinear incremental dynamic analyses. The influential factors on the collapse probabilities of the prototype buildings are found out to specifically suggest the potential modifications of the design requirements. Although the MCE collapse probabilities of all isolated buildings are smaller than those expected for typical non-isolated buildings, these values are significantly different according to the degree of seismicity. The MCE collapse probabilities are dependent upon the governing collapse mechanism and the total system uncertainty. For the prototype buildings located at low-to-moderate seismicity regions, this study proposed the acceptable uncertainty to achieve a similar collapse performance to the corresponding buildings built at high seismicity regions.

Numerical investigation on load transfer mechanism of bonded post-tensioned concrete beam-column substructures against progressive collapse

2020 ◽  
pp. 136943322098165
Author(s):  
Kai Qian ◽  
Hai-Ning Hu ◽  
Yun-Hao Weng ◽  
Xiao-Fang Deng ◽  
Ting Huang
Keyword(s):  
Prestressed Concrete ◽  
Load Transfer ◽  
Numerical Models ◽  
Progressive Collapse ◽  
Load Resistance ◽  
Catenary Action ◽  
Parabolic Profile ◽  
Arch Action ◽  
Column Removal Scenario ◽  
Post Tensioned

This paper presents the high-fidelity finite-element-based numerical models for modeling the behavior of prestressed concrete (PC) beam-column substructures to resist progressive collapse under column removal scenario. After careful calibration against data, the validated numerical models are further employed to shed light on the influence of bonded post-tensioned tendons (BPT) with a parabolic profile on the load transfer mechanisms of PC frames against progressive collapse. The effects of parameters, including initial effective prestress, profile of tendon and lateral constraint stiffness at the beam ends, are also investigated. The study shows that, due to the presence of prestressed tendons, the mobilization of compressive arch action in the beam at small deflections demands stronger lateral constraints, and the ultimate load resistance of PC beam-column substructures depends on combined catenary action from non-prestressed reinforcement and BPT at large deflections. For a given constraint stiffness, the initial effective prestress of BPT has less significant effect on the overall structural behavior. For prestressed tendon, a straight profile usually employed in structural strengthening can improve the initial structural stiffness and yield strength, but is less effective in enhancing the ultimate resistance against progressive collapse than the parabolic profile.

scholarly journals Progressive Collapse Assessment: A review of the current energy-based Alternate Load Path (ALP) method

2019 ◽  
Vol 258 ◽  
pp. 02012 ◽  
Author(s):  
Nur Ezzaryn Asnawi Subki ◽  
Hazrina Mansor ◽  
Yazmin Sahol Hamid ◽  
Gerard Parke
Keyword(s):  
Dynamic Analysis ◽  
Static Analysis ◽  
Progressive Collapse ◽  
Structural Response ◽  
Steel Frame ◽  
Collapse Mechanism ◽  
Load Path ◽  
Acceptance Criterion ◽  
Current Energy ◽  
Collapse Assessment

The Alternate Load Path (ALP) is a useful method that has generated a considerable recent research interest for the assessment of progressive collapse. The outcome of the ALP analysis can be assessed either using the force-based approach or the energy-based approach. The Unified Facilities Criteria (UFC- 4- 023-03) of progressive collapse guideline - have outlined that the force-based approach can either be analysed using static or dynamic analysis. The force-based approach using static analysis is preferable as it does not require a high level of skill and experience to operate the software plus no effort is required in scrutinising the validity of the analysis results output. However, utilising the static approach will eliminate the inertial effect in capturing the actual dynamic response of the collapsed structure. In recent years, the development of the energy-based progressive collapse assessment is attracting widespread interest from researchers in the field; as the approach can produce a similar structural response with the force-based dynamic analysis by only using static analysis. Most of the current energy-based progressive collapse assessments are developed following the requirements which are given in the progressive collapse guidelines provided by the Unified Facilities Criteria. However, little attention is given to the development of the energy-based approach using the Eurocode standards as a base guideline. This article highlights the merits of utilising the energy-based approach against the force-based approach for a collapsed structure and explains the collapse mechanism of a steel frame in the perspective of the energy concept. The state of the art of energy-based progressive collapse assessment for a structural steel frame is reviewed. The comprehensive review will include insights on the development of the energy-based method, assumptions, limitations, acceptance criterion and its applicability with the European standards. Finally, potential research gaps are discussed herein.

Plastic Collapse of a Thin Annular Disk Subject to Thermomechanical Loading

2013 ◽  
Vol 80 (5) ◽  
Author(s):  
Sergei Alexandrov ◽  
Elena Lyamina ◽  
Yeau-Ren Jeng
Keyword(s):  
Analytic Solution ◽  
Hydrostatic Stress ◽  
Yield Criterion ◽  
The Other ◽  
Collapse Mechanism ◽  
Plastic Collapse ◽  
Thermomechanical Loading ◽  
Annular Disk ◽  
Collapse Mechanisms ◽  
Inner Radius

A semi-analytic solution for plastic collapse of a thin annular disk subject to thermomechanical loading is presented. It is assumed that the yield criterion depends on the hydrostatic stress. A distinguished feature of the boundary value problem considered is that there are two loading parameters. One of these parameters is temperature and the other is pressure over the inner radius of the disk. The general qualitative structure of the solution at plastic collapse is discussed in detail. It is shown that two different plastic collapse mechanisms are possible. One of these mechanisms is characterized by strain localization at the inner radius of the disk. The entire disk becomes plastic according to the other plastic collapse mechanism. In addition, two special regimes of plastic collapse are identified. According to one of these regimes, plastic collapse occurs when the entire disk is elastic, except its inner radius. According to the other regime, the entire disk becomes plastic at the same values of the loading parameters at which plastic yielding starts to develop.

Changes of Snow Characteristics During Snowmelt Period and Analysis of Influential Factors - Taking the Juntanghu Watershed in XinJiang as an Example

2012 ◽  
Vol 212-213 ◽  
pp. 395-398
Author(s):  
Hui Wang ◽  
Zhi Hui Liu ◽  
Qiu Dong Zhao
Keyword(s):  
Daily Variation ◽  
Middle Layer ◽  
Bottom Layer ◽  
Atmospheric Temperature ◽  
Influential Factors ◽  
Sudden Increase ◽  
Snowmelt Period ◽  
Acute Change ◽  
Snow Water ◽  
Snow Temperature

Take observational data of March 2011 of study area to analyze changes of snow characteristics during snowmelt period (SP), such as snow grain size (SGS), snow water content (SWC) and snow density (SDS), and to analyze the influential factors. The results show that: SGS decreased during SP, and increased from snow surface layer (SL) to snow bottom layer (BL). That related to the snow depth (SD) and snow temperature (ST). SWC has a sudden increase in late SP. It decreased from snow BL to SL during early and late SP. It has a big daily variation in SL and snow middle layer (ML). It changes hours later than the atmospheric temperature (AT). That related to SD, ST and daily AT. SDS value in SL is the biggest during early SP. It has acute change in SL and a big daily variation in BL .That related to snow age (SA).

scholarly journals Load Carrying and Hydrostatic Performances of Innovative Encapsulated Anchorage System for Unbonded Single Strand

2019 ◽  
Vol 2019 ◽  
pp. 1-16
Author(s):  
Min Sook Kim ◽  
Young Hak Lee
Keyword(s):  
Stress Concentration ◽  
Transfer Test ◽  
Load Transfer ◽  
Maximum Load ◽  
Load Test ◽  
Static Load Test ◽  
Element Analysis ◽  
Bearing Plate ◽  
Anchorage System ◽  
Load Carrying

A new anchorage system is proposed having a circular bearing plate and curvature between the bearing plate and the anchor head to improve stress concentration. A lid with a screw instead of the grouting method is also proposed to prevent moisture penetration. The details of the anchorage device have been chosen to reduce stress concentration based on the finite element analysis. Static load test, load transfer test, and hydrostatic test of fabricated devices were carried out according to ETAG 013 to evaluate the proposed design. As results, the anchorage slip and stabilization satisfied the recommendations of ETAG 013. The maximum load in the load transfer test was at least 1.1 times the ultimate tendon strength. The results of the hydrostatic test showed that the developed anchorage device is watertight to protect against corrosion. As a result of bursting force test, it was confirmed that the proposed anchorage device has more advantages than the conventional rectangular anchorage devices in terms of stress distribution.

Seismic Vulnerability of Ancient Churches: I. Damage Assessment and Emergency Planning

2004 ◽  
Vol 20 (2) ◽  
pp. 377-394 ◽  
Author(s):  
Sergio Lagomarsino ◽  
Stefano Podestà
Keyword(s):  
Damage Assessment ◽  
Seismic Behavior ◽  
Seismic Vulnerability ◽  
Collapse Mechanism ◽  
Damage Level ◽  
Bell Tower ◽  
Collapse Mechanisms ◽  
Damage Grades ◽  
Definition Of ◽  
The Church

This paper describes a new methodology used to assess seismic damage in the churches of Umbria and the Marches, which is based on 18 indicators, each representative of a possible collapse mechanism for a macroelement. The subdivision of the church into macroelements consists of the identification of architectonic elements in which the seismic behavior is almost independent from the rest of the structure (façade, apse, dome, bell tower, etc.). For each macroelement, by considering its typology and connection to the rest of the church, it is possible to identify the damage modes and the collapse mechanisms. During inspection operations, the surveyors must indicate: (a) the actual macroelements; (b) the damage level; and (c) the vulnerability of the church to that mechanism, related to some specific details of construction. From these data a damage score is defined, which is a number from 0 to 1, obtained as a normalized mean of the damage grades in each mechanism. The analysis of the collected data (more than 1,000 churches in Umbria) allows the definition of the correlation between macroseismic intensity and damage.

scholarly journals Functional Catastrophe Analysis of Collapse Mechanism for Shallow Tunnels with Considering Settlement

2016 ◽  
Vol 2016 ◽  
pp. 1-11 ◽  
Author(s):  
Rui Zhang ◽  
Hai-Bo Xiao ◽  
Wen-Tao Li
Keyword(s):  
Failure Criterion ◽  
Virtual Work ◽  
Underground Water ◽  
Collapse Mechanism ◽  
Upper Bound Theorem ◽  
Geomechanical Properties ◽  
Shallow Tunnels ◽  
Collapse Mechanisms ◽  
Functional Catastrophe Theory ◽  
The Stability

Limit analysis is a practical and meaningful method to predict the stability of geomechanical properties. This work investigates the pore water effect on new collapse mechanisms and possible collapsing block shapes of shallow tunnels with considering the effects of surface settlement. The analysis is performed within the framework of upper bound theorem. Furthermore, the NL nonlinear failure criterion is used to examine the influence of different factors on the collapsing shape and the minimum supporting pressure in shallow tunnels. Analytical solutions derived by functional catastrophe theory for the two different shape curves which describe the distinct characteristics of falling blocks up and down the water level are obtained by virtual work equations under the variational principle. By considering that the mechanical properties of soil are not affected by the presence of underground water, the strength parameters in NL failure criterion can be taken to be the same under and above the water table. According to the numerical results in this work, the influences on the size of collapsing block different parameters have are presented in the tables and the upper bounds on the loads required to resist collapse are derived and illustrated in the form of supporting forces graphs that account for the variation of the embedded depth and other factors.

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