Cantilever Wall Research Articles

Energy conservation validates deformation mechanisms around model cantilever wall excavations in sand

Based on soil movement measurements in two centrifuge models simulating cantilever wall excavation in dense and loose sand respectively, simplified deformation mechanisms are proposed on both sides of the wall. Negative dilation angles are used in the mechanism to model sand volume change at a moderate strain level corresponding with the typical serviceability limit of facilities on the retained ground within the zone of influence of the wall. An energy calculation is then performed for each of the two centrifuge tests to check the internal consistency of the inferred deformation mechanisms, and the adequacy of the stress–strain model used for the sand. It is found that energy balances within an error of 7% in both tests. The major energy flow happens on the active side of the wall, where the potential energy loss is roughly equal to the work done due to sand shear and contraction. The energy stored in wall bending and the energy lost due to boundary friction are small in comparison. The validated model of the settlement and shearing of the retained ground is then used to illustrate how to assess the degree of building damage in relation to angular distortion and tensile strain in the retained ground supporting its shallow foundations.

Dynamic Behavior of Rocking and Hybrid Cantilever walls in Precast Concrete Building

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중력식 구조물의 형태에 따른 주동토압 산정과 설계법 제안

In this study theories of earth pressure such as Rankine, Coulomb, Trial Wedge, Improved Trial Wedge, used in the design for onshore and offshore structures, are analyzed and the characteristics of loaded pressure to virtual back (wall, plane) and wall surface in accordance with the structure type are suggested. To investigate characteristics of earth pressure, gravity retaining wall with inclined angle and cantilever wall with inclined ground are movilized for onshore structures and caisson and block type quay wall are mobilized for offshore structures. Based on various theories, the earth pressure applied angle(wall friction angle) and sliding angle toward the wall, which is influenced by the heel length, are calculated and compared. In the case of long heel, the pressure by Rankine`s method in virtual plane and the mobilized angle are most reasonably estimated by the ground slope, and in the case of short heel, the pressure by Coulomb`s method and the mobilized angle by the angle of wall friction. In addition, the sliding angle toward the wall estimated by the improved trial wedge method is large than the value of Rankine`s method. Finally, in this study the reasonable method for calculating the pressure and the mobilized angle that can be applied to the routine design of port structures is proposed. The proposed method can decide the earth pressure with length of a heel and a self weight of retaining wall according to sliding angle toward the wall.

Backfill and subsoil interaction effects on seismic behavior of a cantilever wall

The main focus of the current study is to evaluate the dynamic behavior of a cantilever retaining wall considering backfill and soil/foundation interaction effects. For this purpose, a three-dimensional finite element model (FEM) with viscous boundary is developed to investigate the seismic response of the cantilever wall. To demonstrate the validity of the FEM, analytical examinations are carried out by using modal analysis technique. The model verification is accomplished by comparing its predictions to results from analytical method with satisfactory agreement. The method is then employed to further investigate parametrically the effects of not only backfill but also soil/foundation interactions. By means of changing the soil properties, some comparisons are made on lateral displacements and stress responses. It is concluded that the lateral displacements and stresses in the wall are remarkably affected by backfill and subsoil interactions, and the dynamic behavior of the cantilever retaining wall is highly sensitive to mechanical properties of the soil material.

Seismic shear distribution among interconnected cantilever walls of different lengths

SUMMARYMid‐rise to high‐rise buildings in seismic areas are often braced by slender reinforced concrete (RC) walls, which are interconnected by RC floor diaphragms. In design, it is typically assumed that the lateral forces are distributed in proportion to the wall's elastic stiffness. Pushover analyses of systems comprising walls of different lengths have, however, shown that large compatibility forces can develop between them, which should be considered in design, but the analyses have also shown that the magnitude of the computed forces is very sensitive to the modelling assumptions. Using the results of a complex shell element model as benchmark, different simple hand‐calculation methods and inelastic beam element models are assessed and improved to yield reliable estimates of the base shear distribution among the individual walls comprising the interconnected wall system. Copyright © 2014 John Wiley &amp; Sons, Ltd.

Influence of wall flexibility on dynamic response of cantilever retaining walls

A seismic evaluation is made of the response to horizontal ground shaking of cantilever retaining walls using the finite element model in three dimensional space whose verification is provided analytically through the modal analysis technique in case of the assumptions of fixed base, complete bonding behavior at the wall-soil interface, and elastic behavior of soil. Thanks to the versatility of the finite element model, the retained medium is then idealized as a uniform, elastoplastic stratum of constant thickness and semi-infinite extent in the horizontal direction considering debonding behavior at the interface in order to perform comprehensive soil-structure interaction (SSI) analyses. The parameters varied include the flexibility of the wall, the properties of the soil medium, and the characteristics of the ground motion. Two different finite element models corresponding with flexible and rigid wall configurations are studied for six different soil types under the effects of two different ground motions. The response quantities examined incorporate the lateral displacements of the wall relative to the moving base and the stresses in the wall in all directions. The results show that the wall flexibility and soil properties have a major effect on seismic behavior of cantilever retaining walls and should be considered in design criteria of cantilever walls. Furthermore, the results of the numerical investigations are expected to be useful for the better understanding and the optimization of seismic design of this particular type of retaining structure.

Evaluation of the effect of lateral soil pressure on cantilever retaining wall with soil type variation

Retaining wall is defined as a structure with a main purpose to prevent lateral movement, retain earth or water and may role to support vertical loads. There are several types of retaining wall and the most common types used are gravity wall, cantilever wall, counterfort walls and buttressed wall. Therefore, a few components need to be used in order to get the objective. As a result, this system can be used for the design of a cantilever retaining wall. Moreover, it saves time in the design with sufficient layout detail of the cantilever retaining wall. Design of cantilever retaining walls involves stability checks for overturning, sliding and bearing. A trial section is assumed and calculations are made for the stability checks. The important parameters involved are unit weight of backfill soil, stem height and concrete type. The base length and it components namely toe land heel lengths, and base thickness are highly dependent upon these factors and vary sharply with stem height. The trial section geometry for a given wall height, soil data and strength of concrete can be examine from these charts and final section profile may be determined within a minimum time. The charts have been prepared for a wide range of values of soil unit weight, moment.

Seismic Performance Research of Viscous Dampers under Different Arrangement

This paper introduces a variety of viscous damper installation form, including brace, herringbone and cantilever wall installation. By an example, install the bracing form, herringbone installation form and type cantilever wall installation condition are compared, And to calculate the results of its damping effect has carried on the comparative study, The superiority of the cantilever wall type layout pattern is obtained.

Some remarks on the seismic behaviour of embedded cantilevered retaining walls

This paper is a numerical investigation of the physical phenomena that control the dynamic behaviour of embedded cantilevered retaining walls. Recent experimental observations obtained from centrifuge tests have shown that embedded cantilevered retaining walls experience permanent displacements even before the acceleration reaches its critical value, corresponding to full mobilisation of the soil strength. The motivation for this work stems from the need to incorporate these observations in simplified design procedures. A parametric study was carried out on a pair of embedded cantilevered walls in dry sand, subjected to real earthquakes scaled at different values of the maximum acceleration. The results of these analyses indicate that, for the geotechnical design of the wall, the equivalent acceleration to be used in pseudo-static calculations can be related to the maximum displacement that the structure can sustain, and can be larger than the maximum acceleration expected at the site. For the structural design of the wall, it is suggested that the maximum bending moments of the wall can be computed using a realistic distribution of contact stress and a conservative value of the pseudo-static acceleration, taking into account two-dimensional amplification effects near the walls.

주문진 모래를 이용한 선반식 옹벽의 수평토압 측정 모형시험

최근 국내에서도 구조물의 안정성을 향상시키고 수평토압의 크기를 줄여주는 선반식 옹벽에 대한 관심이 높아지고 있다. 이에 따라 모형시험 등 연구도 수행되기 시작했는데 기존 모형시험은 시험조건도 다양하지 않으며, 시험방법 등에서 개선해야 할 점이 있다. 이 연구에서는 개선된 모형시험 방법으로 여러 가지 다양한 조건에 대하여 모형시험을 수행하여 선반식 옹벽의 수평토압 감소효과를 확인하고자 하였다. 모형지반으로는 옹벽모형지반으로 일반적으로 많이 사용되는 주문진 모래를 이용하였으며, 1.2m의 모형옹벽을 15개 층으로 나누어 층마다 2개씩 총 30개의 로드셀을 사용하여 옹벽 높이별 수평토압을 측정하였다. 연구결과 선반식 옹벽은 캔틸레버식 옹벽에 비해 수평토압이 작게 발생하였으며, 선반 길이, 선반위치 등에 따라 수평토압의 크기가 영향을 받는 것으로 나타났다. Recently, the retaining wall with the relieving platform has received increasing interests also in Korea in that it can reduce the lateral earth pressure and provide more stability than conventional retaining wall. Previous studies with model tests studies covered only a limited test conditions. In this study, total 15 model tests were performed for various conditions with improved model test apparatus to confirm the effect of decreasing the lateral earth pressure on the retaining wall with the relieving platform. Jumoonjin sand was used for model soil and 2 load cells were used for each 15 layers to measure the lateral earth pressure. Based on the experimental results, the lateral earth pressure of the retaining wall with the relieving platform is less than the that of cantilever wall. The length of the platform and the location of the platform are the key factors influencing the lateral earth pressure.

DISPLACEMENT MONITORING AND SENSITIVITY ANALYSIS IN THE OBSERVATIONAL METHOD

Abstract This work discusses the fundamentals of designing deep excavation support by means of observational method. The effective tools for optimum designing with the use of the observational method are both inclinometric and geodetic monitoring, which provide data for the systematically updated calibration of the numerical computational model. The analysis included methods for selecting data for the design (by choosing the basic random variables), as well as methods for an on-going verification of the results of numeric calculations (e.g., MES) by way of measuring the structure displacement using geodetic and inclinometric techniques. The presented example shows the sensitivity analysis of the calculation model for a cantilever wall in non-cohesive soil; that analysis makes it possible to select the data to be later subject to calibration. The paper presents the results of measurements of a sheet pile wall displacement, carried out by means of inclinometric method and, simultaneously, two geodetic methods, successively with the deepening of the excavation. This work includes also critical comments regarding the usefulness of the obtained data, as well as practical aspects of taking measurement in the conditions of on-going construction works.

Modelling shear–flexure interaction in equivalent frame models of slender reinforced concrete walls

SUMMARYQuasi‐static cyclic tests on reinforced concrete (RC) walls have shown that shear deformations can constitute a significant ratio of the total deformations when the wall is loaded beyond the elastic regime. For slender RC walls that form a stable flexural mechanism, the ratio of shear to flexural deformations remains approximately constant over the entire range of imposed displacement ductilities. This paper proposes a method for incorporating shear‐flexure interaction effects in equivalent frame models of slender RC walls by coupling the shear force‐shear strain relationship to the curvature and axial strain in the member. The suggested methodology is incorporated in a finite element consisting of two interacting spread inelasticity sub‐elements representing flexural and shear response, respectively. The element is implemented in the general finite element code IDARC and validated against experimental results of RC cantilever walls. In a second step, it is applied in inelastic static and dynamic analyses of tall wall and wall‐frame systems. It is shown that ignoring shear‐flexure interaction may lead to erroneous predictions in particular of local ductility and storey drift demands. Copyright © 2013 John Wiley &amp; Sons, Ltd.

Prediction of failure of a cantilever–wall connection using post-installed rebars under thermal loading

Polymer based mortars allow post-installing rebars into pre-existing concrete structures by bonding the steel to the concrete in a few hours. This type of steel–polymer–concrete bond may show similar performances to classic rebar–concrete connections at ambient temperature but, due to the adhesive layer, it tends to lose rapidly its load bearing capacity at higher temperatures which raises the issue of fire safety for these types of structural connections. This paper presents a simple model for estimating the time before collapse in a structure subjected to fire according to ISO 834-1 heating. Entry data for the ultimate load calculation is obtained through pull-out tests performed at different temperatures on small size samples made out of concrete cylinders in order to obtain an ultimate bond stress–temperature relationship. Model predictions are then compared to data from a full scale test made out of a wall–cantilever connection using post-installed rebars. The connection is thermally loaded in a gas furnace up to collapse of the cantilever due to the slip of the chemically bonded rebar. Temperature and displacement measurements during the test are analyzed in order to evaluate the accuracy of this method in safely estimating the ultimate temperature and stress distribution along the bond just before failure.

Yield Displacement Calculation Method of High-Strength Concrete Shear Wall

Considering high compressive strength of high-strength concrete, it is assumed that concrete compressive stress of the cross-section compression zone is linear distribution when the cross-section of high-strength concrete shear wall reaches yield situation. Based on the plane section assumption, the yield curvature formula of shear wall section is obtained by using moment - curvature analysis method. The parameters effecting yield curvature of high-strength concrete shear wall are studied by using the yield curvature formula. The results show that longitudinal reinforced yield strain is the most influencing factor of the yield curvature in addition to axial load ratio. This paper presents yield curvature formula considering the impact of axial load ratio and boundary reinforcement yield stress through the regression analysis of calculation results. On this basis, the vertex yield displacement formula of high-strength concrete shear wall is proposed, and the calculation results of formula correspond to the vertex yield displacement experimental values of the 12 high-strength concrete cantilever wall well.

An Improved Puncture Access Tip-Retraction Mechanism

An Improved Puncture Access Tip-Retraction Mechanism

Seismic shear forces on RC walls: review and bibliography

Effect of higher vibration modes on the seismic shear demand of reinforced concrete cantilever walls has been studied since the 1970’s. The shear amplification becomes more important with increasing fundamental period (tall buildings) and increasing ductility demand (R or q factors). Yet, studying the relevant recommendations of structural engineering researchers and provisions of various seismic codes reveals that there is no consensus regarding the extent of shear amplification and of the inter-wall distribution of shear demand in structural systems comprising walls of different lengths. The paper presents the available formulas for predicting shear amplification in ductile walls and dual systems (wall-frames). One effect that impacts the shear amplification is shear cracking mainly in the plastic hinge zone of the wall near the base leading to appreciably lower shear amplification than previously predicted. Post yield shear redistribution among interconnected unequal walls is also addressed. Finally, an extensive bibliography is provided.

Lateral earth pressures on flexible cantilever retaining walls with deformable geofoam inclusions

The present study explores the potential application of geofoam in reducing the lateral earth pressures on flexible cantilever walls retaining cohesionless and dry backfills. Results of 1-g physical model tests addressing the behavior of yielding cantilever retaining walls with expanded polystyrene (EPS) and extruded polystyrene (XPS) geofoam compressible inclusions are discussed. The effect of relative flexibility of the wall as well as the characteristics of the cohesionless backfill and geofoam on the active earth pressures were investigated in this context. A finite difference code was validated against the lateral earth pressures and backfill strains observed in the tests. Experimental results indicate that the shape of active pressure distribution diagram behind a cantilever retaining wall is non-linear and varies depending on the wall flexibility and characteristics of deformable layer. Geofoam inclusions provide reduction in lateral earth pressures, however the positive contribution of the compressible buffer decreases as wall relative flexibility increases. Reduction of the lateral earth loads is associated with the formation of a wider, non-linear and more stable failure zone induced from the combined influence of the flexural deformations of the cantilever wall and the arching effect induced at the lower half portion of the cohesionless backfill retained by the flexible wall-deformable panel system. Parametric numerical analyses were performed to extend the predictions of the lateral earth pressure coefficients for various combinations of backfill, deformable inclusion and structural attributes by validated numerical model. Based on the results of the parametric analyses, design charts and regression models were proposed to predict active lateral earth pressure coefficients and point of application of the lateral load on the flexible cantilever earth retaining walls with and without deformable geofoam layers.

Evaluation of the effect of earthquake frequency content on seismic behavior of cantilever retaining wall including soil–structure interaction

A three-dimensional backfill–structure–soil/foundation interaction phenomenon is simulated using the finite element method in order to analyze the dynamic behavior of cantilever retaining wall subjected to different ground motions. Effects of both earthquake frequency content and soil–structure interaction are evaluated by using five different seismic motions and six different soil types. The study mainly consists of three parts. In the first part, following a brief review of the problem, the finite element model with viscous boundary is proposed under fixed-base condition. In the second part, analytical formulations are presented by using modal analysis technique to provide the finite element model verification, and reasonable agreement is found between numerical and analytical results. Finally, the method is extended to further investigate parametrically the effects of not only earthquake frequency content but also soil/foundation interaction, and nonlinear time history analyzes are carried out. By means of changing the soil properties, some comparisons are made on lateral displacements and stress responses under different ground motions. It is concluded that the dynamic response of the cantilever wall is highly sensitive to frequency characteristics of the earthquake record and soil–structure interaction.

Retaining wall behaviour in Dublin's estuarine deposits, Ireland

Practising engineers in the Dublin, Ireland, area have much experience in dealing with the boulder clay which underlies much of the city. However, significant deposits of estuarine soils, some of them soft, exist along the east side of the city and in particular in Dublin docklands. Some construction difficulties have previously been encountered in these materials and significant developments, including a large tunnel project, are planned in the area overlying these deposits. Few published data exist on retaining wall schemes in the deposits. Data from nine sites, including three detailed case histories, are presented which confirm that construction of deep propped excavations and cantilever walls up to 7·5 m are feasible in these deposits and can perform well. A key issue is the soil that is located at excavation level and competent deposits here are essential to prevent large displacements or possible instability. The resulting movement will also be sensitive to the overall system stiffness. There seems to be scope for more efficient future design, including more use of cantilever walls, particularly for temporary works purposes. Beam-on-spring type computer analyses tend to give conservative results for these deposits and more sophisticated finite-element analyses may be warranted for future schemes.

Deformation Limits for Structural Walls with Confined Boundaries

For accurate analytical assessment of performance and damage in reinforced concrete members, well-defined deformation limits at particular damage states are required. With advanced and computationally intensive finite element analyses, we establish deformation limits at yield and ultimate limit states for adequately confined rectangular reinforced concrete structural walls in terms of drift ratio, plastic rotation, and curvature. To investigate the deformation limits of structural walls, a parametric study on isolated cantilever wall models is performed. The primary variables of the parametric study are the shear-span-to-wall-length ratio, wall length, axial load ratio, normalized shear stress, the amount of horizontal web reinforcement, and the amount of longitudinal reinforcement at the confined boundary of structural wall models. Expressions and limit values are proposed for yield and ultimate deformation capacity of structural walls, based on the most influential parameters. The proposed equations are found to be promising when compared to results of experiments.