Numerical simulation on the seismic performance of retrofitted masonry walls based on the combined finite-discrete element method

Due to the long construction life,improper design methods,brittle material properties and poor construction techniques,most existing masonry structures do not perform well during earthquakes.The retrofitting method using an external steel-meshed mortar layer is widely used to retrofit existing masonry buildings.Assessing the seismic performance of masonry walls reinforced by an external steel-meshed mortar layer reasonably and effectively is a difficult subject in the research field of masonry structures.Based on the combined finite-discrete elements method,the numerical models of retrofitted brick walls with four different masonry mortar strengths by an external mortar layer are established.The shear strength of mortar and the contact between the retrofitted mortar layer and the brick blocks are discussed in detail.The failure patterns and load-displacement curves of the retrofitted brick walls were obtained by applying low cycle reciprocating loads to the numerical model,and the bearing capacity and the failure mechanism of the retrofitted walls were obtained by comparing the failure patterns,ultimate bearing capacity,deformability and other aspects with the tests.This study provides a basis for improving the seismic strengthening design method of masonry structures and helps to better assess the seismic performance of masonry structures after retrofitting.

The contribution of steel wallposts to out-of-plane behavior of non-structural masonry walls

For years,non-structural masonry walls have received little attention by code developers and professional engineers.Recently,significant efforts have been made to shed more light on out-of-plane(OOP)behavior of non-structural masonry walls.In updated provisions of the Iranian seismic code,bed joint reinforcements(BJRs)and steel wallposts have been suggested for use.BJRs are horizontal reinforcements;steel wallposts are vertical truss-like elements intended to provide additional OOP restraints for a wall.The contribution of BJRs has previously been investigated by the authors.This study is devoted to investigating the contribution of steel wallposts to the OOP behavior of non-structural masonry walls.Using pre-validated 3D finite element(FE)models,the OOP behavior of 180 non-structural masonry walls with varying configurations and details are investigated.The OOP pressure-displacement curve,ultimate strength,the response modification factor,and the cracking pattern are among the results presented in this study.It is found that steel wallposts,especially those with higher rigidity,can improve the OOP strength of the walls.The contribution of wallposts in the case of shorter length walls and walls with an opening are more pronounced.Results also indicate that masonry walls with wallpost generally have smaller modification factors compared to similar walls without wallpost.

Experimental studies on behavior of fully grouted reinforced-concrete masonry shear walls

An experimental study is conducted on fully grouted reinforced masonry shear walls (RMSWs) made from concrete blocks with a new configuration. Ten RMSWs are tested under reversed cyclic lateral load to investigate the influence of different reinforcements and applied axial stress values on their seismic behavior. The results show that flexural strength increases with the applied axial stress, and shear strength dominated by diagonal cracking increases with both the amount of horizontal reinforcement and applied axial stress. Yield displacement, ductility, and energy dissipation capability can be improved substantially by increasing the amount of horizontal reinforcement. The critical parameters for the walls are derived from the experiment: displacement ductility values corresponding to 15% strength degradation of the walls reach up to 2.6 and 4.5 in the shear and flexure failure modes, respectively; stiffness values of flexure- and shear-dominated walls rapidly degrade to 17%–19% and 48%–57% of initial stiffness at 0.50 Dmax (displacement at peak load). The experiment suggests that RMSWs could be assigned a higher damping ratio (～14%) for collapse prevention design and a lower damping value (～7%) for a fully operational limit state or serviceability limit state.

Blast response of clay brick masonry unit walls unreinforced and reinforced with polyurea elastomer

Clay brick masonry unit(CBMU) walls are widely used in building structures,and its damage and protection under explosion loads have been a matter of concern in the field of engineering protection.In this paper,a series of full-scale experiments of the response characteristics of 24 cm CMBU walls unreinforced and reinforced with polyurea elastomer subjected to blast loading were carried out.Through setting 5.0 kg TNT charges at different stand-off distances,the damage characteristics of masonry walls at different scaled distances were obtained.The reinforcement effect of different polyurea coating thicknesses and methods on the blast resistance performance of masonry walls under single and repeated loads were also explored.Five failure grades were summarized according to the dynamic response features of masonry walls.Based on the stress wave propagation pattern in multi-media composite structures,the internal stress distribution of masonry walls were analyzed,and the division basis of the masonry walls’ failure grades was then quantified.Combined with Scanning Electron Microscope(SEM)images,the deformation characteristics of soft and hard segments of polyurea and effects of detonation products on microstructures were revealed respectively,which provides an important reference for the design and application of polyurea in the blast resistance of clay brick masonry walls.

Performance of masonry enclosure walls:lessons learned from recent earthquakes

This paper discusses the issue of performance requirements and construction criteria for masonry enclosure and infill walls. Vertical building enclosures in European countries are very often constituted by non-load-bearing masonry walls, using horizontally perforated clay bricks. These walls are generally supported and confined by a reinforced concrete frame structure of columns and beams/slabs. Since these walls are commonly considered to be nonstructural elements and their influence on the structural response is ignored, their consideration in the design of structures as well as their connection to the adjacent structural elements is frequently negligent or insufficiently detailed. As a consequence, nonstructural elements, as for wall enclosures, are relatively sensitive to drift and acceleration demands when buildings are subjected to seismic actions. Many international standards and technical documents stress the need for design acceptability criteria for nonstructural elements, however they do not specifically indicate how to prevent collapse and severe cracking, and how to enhance the overall stability in the case of moderate to high seismic loading. Furthermore, a review of appropriate measures to improve enclosure wall performance and both in-plane and out-of-plane integrity under seismic actions is addressed.

Development of a monitoring and warning system based on optical fiber sensing technology for masonry retaining walls and trees

Hong Kong has a long history of applying masonry retaining walls to provide horizontal platforms and stabilize man-made slopes.Due to the sub-tropical climate,some masonry retaining walls are colonized by trees.Extreme weather,such as typhoons and heavy rains,may cause rupture or root failure of those trees,thus resulting in instability of the retaining walls.A monitoring and warning system for the movement of masonry retaining walls and sway of trees has been designed with the application of fiber Bragg grating(FBG)sensing technology.The monitoring system is also equipped with a solar power system and 4G data transmission devices.The key functions of the proposed monitoring system include remote sensing and data access,early warning,and real-time data visualization.The setups and working principles of the monitoring systems and related transducers are introduced.The feasibility,accuracy,serviceability and reliability of this monitoring system have been checked by in-site calibration tests and four-month monitoring.Besides,a two-level interface has been developed for data visualization.The monitoring results show that the monitored masonry retaining wall had a reversible movement up to 2.5 mm during the monitoring period.Besides,it is found that the locations of the maximum strain on trees depend on the crown spread of trees.

Experimental Investigation on Flexural Performance of Masonry Walls Reinforced with GFRP

This paper presents the results of a test program for flexure reinforcing characteristics of gless fiber-rein forced polymer（GFRP） sheets bonded to masonry beams. A total of eight specimens subjected to monotonic four-point bending were tested up to failure. These specimens were constructed with two different bond patterns. Six of these specimens were reinforced by using GFRP sheets prior to testing, and the remaining two were not reinforced. The test results indicate a significant increase in both load-bearing capacity and ductile performance of the reinforced walls over the unreinforced ones.

Failure criteria of unreinforced masonry walls of rural buildings under the impact of flash floods in mountainous regions

Damage to rural buildings in mountainous regions caused by flash floods accounts for a significant proportion of economic losses from disasters.The unreinforced masonry(URM)wall is the most vulnerable structural element of rural buildings exposed to flash floods.The failure of a URM wall indicates damage to rural buildings in flash floods.Based on the yield line theory of out-of-plane damage of URM walls and the virtual work method,brittle failure criteria for URM walls under the impact of flash floods were established.According to the field investigation data of the 26 June 2020 flash flood event in Damawu Gully and the corresponding simulation results of FLO-2D,the disaster-causing process was analysed,and the failure criteria were validated.Three building parameters were identified to influence the flood-resistance of URM walls,including the mortar grade,the span-to-height ratio of the wall,and the number of floors of the rural building.The results showed that the cause of the 26June disaster was the diversion of a 50-year flash flood into the residential community on the alluvial fan.The affected buildings were constructed with hollow blocks and lacked flood-resistance reinforcement.The critical failure depth of a URM wall restrained at the top by ring beams(RBs)under hydrostatic load conditions is 1.17 to 1.20 times greater than that of a URM wall without RBs,and the difference is even more pronounced when lowerstrength mortar is used.The flood-resistance of a URM wall constructed with Mb 7.5 mortar and restrained by RBs is almost as strong as that of a URM wall constructed with Mb 20 mortar and without RBs.The span-to-height ratio of a URM wall should not be greater than 1.875 in this case.However,the flood-resistance of a URM wall with RB restraint is almost independent of the span-to-height ratio.The brittle fracture energy of masonry mortar is more crucial to the flood-resistance of 4-edge restrained URM walls if L/Z>1.875.The flood-resistance of the URM wall of the first storey increases linearly with the number of floors.Single-storey rural buildings should be given priority to the use of high-grade masonry mortar and high-density blocks to improve flood-resistance.The failure criteria and the influence laws of building parameters on the flood-resistance of URM walls can provide references for flash flood mitigation and flood-resistance reinforcement of rural buildings in mountainous regions of Southwest China.

Experimental Study on Properties of Masonry Infill Walls Connected to Steel Frames with Different Connection Details

The properties of infills and the way they are connected to frames may have significant effects on the seismic behavior of the structure.This study pre-sents an experimental study on evaluation and testing of five single story,single bay samples with the scale 1:3.This study strives to evaluate the behavior of masonry infill walls encased in steel frames,with emphasis on diferent details of the connection of the wall to the frame.Four frames with masonry infills and one frame without infill are experimented on by apply ing lateral load to their upper beams.Different details of the connection between the infill and the frame including anchorless wall within the frame,connecting the frame and the infill using separating vertical angles,steel rebars embedded in the infill wall and also using Added Damping And Siffness(ADAS)elements between the infill and the frame were investigated.The results indicate that the manner in which the infill and the frame are connected not only can significantly affect the crack fomation pattern and the failure modes of the infill wall,it's also alters the stiffness,the strength,the ductility,the out-of-plane deformation,and the amount of energy dis-sipation of the frame.Furthermore,not only using the ADAS yielding damper in the connection between the infill and the frame increases ductility and prevents the load-displacement diagram from plummeting,it also can be used in regions with medium to high relative seismic risk given that it can be replaced after the occurrence of earthquakes.

Numerical Modeling and Analysis of Unreinforced Masonry Walls

Estimation of shear strength and other mechanical characteristics of masonry wall panels through experimental research is the most reliable analysis approach. However, considering all the difficulties in performing experimental research, material costs, laboratory preparations and time expenses, it is not difficult to conclude that this approach is also not the most rational. Aside from experimental investigations, advanced analytical methods are considered cheaper and practical, which can approximately describe the mechanical behavior of masonry walls. The aim of this chapter is to demonstrate how advanced analytical methods, based on discrete and applied element methods, are capable of estimating, in close approximation, the realistic behavior of masonry walls. The use of advanced analysis methods for determination of the behavior of full-scaled masonry walls （with and without openings）, avails the inclusion of infill masonry walls on the processes of modeling, analysis and design of building structures, without the need of extensive experimental investigations. This would result in achieving more approximate analytical building models in respect to their realistic behavior and ultimately achieve better optimization of structural design.

Comparison Research of Bed Joints Construction and Bed Joints Reinforcement on Shear Parameters of AAC Masonry Walls

The work presents the results of tests on the shear parameters of walls made of AAC （autoclaved aerated concrete, fb = 4.0 N/mm2） on the system mortar for thin M5 and M10 joints （fm = 6.1 N/mm2 and fro = 11.9 N/mm2） and on polyurethane glue and also walls without mortar （dry masonry）. The wall compression strength （on mortar M5 class） （per EN 1052-1：2000） amounted tofc,mv= 2.97 N/mm2 （fk = 2.48 N/mm2）, elastic modulus was Ecru = 2,040 N/mm2. Various structure of bed joints and head joints were applied and the following were used as reinforcement： steel trusses of EFZ 140/Z 140 type （Z1 type） and meshes made of plastics （Z2 type）. Based on the tests carried out with regard to unreinforced elements, it was shown that the filling in of head joints with mortar had an advantageous effect on the values of cracking and destruction stresses. While, with the use of reinforcement, advantageous increase of stress was obtained only when the mortar was laid twice on both bed surfaces of masonry units. The application of reinforcement in the bed joints when the mortar was laid only on one bed joints surface of the masonry units reduced the values of cracking and destruction stresses in relation to the values obtained in the unreinforced walls.

Experimental Study on Improving Seismic Behavior of Load-Bearing Masonry Wall Made of Autoclaved Aerated Concrete

To investigate the seismic behavior of autoclaved aerated concrete load-bearing masonry wall(AACLMW), a piece of control block wall without constructional measures and five pieces of block walls with different constructional measures were tested under low reversed cyclic loading which imitated low to moderate earthquake force. The seismic behavior of AACLMW with different constructional measures in terms of failure mode, hysteretic curve, deformation capacity and displacement ductility was studied and compared with that without constructional measures. The experimental results indicate that the constructional measures comprising constructional columns and horizontal concrete strips are effective for improving the seismic behavior of AACLMW. The study in this paper can provide a reliable experimental basis for further analysis and engineering application of AACLMW in the future.

Modelling of URM Walls Retrofitted with Cable: A Comparison Between a Basic Mechanical Model and Distinct Element Method

The Australian love of 'heritage' buildings (most of them are unreinforced masonry (URM)) means that greater attention is required to secure their performance under seismic or impact loading in the future. A research project has been carried out to develop a new, economic and high strength retrofitting technique for masonry structures. A series of experimental testing on URM walls retrofitted with an innovative technique by cable system have been conducted. In this paper, an analytical model which is based on distinct element method (DEM) is developed to simulate the behaviour of retrofitted walls. In DEM, a solid is represented as an assembly of discrete blocks. Joints are modelled as interface between distinct bodies. It is a dynamic process and specially designed to model the behaviour of discontinuities. In order to assist the practising engineers to design this new retrofitted wall system, a simple mechanical model was also developed to predict the strength of the retrofitted walls. The results obtained from this simple mechanical model are compared with those from both experiments and distinct element model.

Numerical Prediction of Statistical Masonry Wall Fragment Distribution Induced by Blast Loading

The hazard caused by the fragments of damaged structures is usually significant in acci-dental explosions or hostile blast events.A reliable and efficient method to estimate probable fragment size,velocity and launch distance will be useful to assess and design countermeasures to mitigate the possible fragment hazards.This paper presents a numerical method for predicting the size and launch distance of the fragments caused by explosive damage of masonry wall.Numerical simulations with different scaled distances are carried out,and the statistical distribution functions of the fragment size and launch distance in terms of the scaled distance are derived.

考虑非结构构件的木结构古建筑抗震性能研究综述

木结构古建筑是我国文物建筑的主体,它以木材为主要承重构件,具有深厚的历史文化价值。本文根据已有研究,从结构试验、数值模拟、抗震性能评估方法 3个方面,总结了含有隔墙、隔扇、雀替等非结构构件的古木建筑抗震性能研究现状。研究表明,非结构构件可以限制榫卯节点拔榫,改善节点受力,不同程度提高结构的强度、刚度和耗能能力,降低了结构在地震作用下坍塌的概率。最后结合我国木结构古建筑的研究现状以及与其他国家的研究差异,给出了未来木结构古建筑抗震性能的可能研究方向。

CFRP-聚合物砂浆加固震损构造柱约束砖砌体墙试验研究

为研究斜向碳纤维布条带或斜向聚合物砂浆条带与外覆角钢组合的加固方式对震后砌体结构的加固效果,对模拟经过地震作用的三面带构造柱约束砌体墙片进行抗震加固,并进行拟静力试验。三面砌体墙均采用角钢外覆加固,面层采用不同方式处理。研究结果表明:采用碳纤维布-聚合物砂浆条带的加固方式能很好地恢复震损墙体的承载能力和变形能力;碳纤维布条带在限制裂缝开展以及提高震损结构延性方面有一定贡献;面层采用斜向聚合物砂浆条带加固的震损墙体延性和承载力均较低。工程实际应用中,建议考虑两种材料的复合加固形式。

改进锚固的钢丝绳-聚合物砂浆交叉条带加固砌体墙拟静力试验研究

本文基于新的钢丝绳锚固方式和墙体构造措施,进行了5片砌体墙的抗震拟静力试验,其中4片采用钢丝绳-聚合物砂浆交叉条带法加固,1片未加固墙作为对照组。综合前期已有试验数据,推导钢丝绳-聚合物砂浆交叉条带法加固砌体墙的抗剪承载力公式。试验表明:改进锚固方式后的交叉条带法在构造上更为可靠,能有效提高砌体墙抗剪承载力,组合墙体承载力较未加固墙提高65%以上,较旧锚固法承载力平均可提高30%;交叉条带对墙体裂缝的出现和发展有一定限制作用,使得墙体的延性有所提高;受力时条带拉压杆体系与原有墙体之间的协同效应能有效提高承载力。最后根据8片墙拟合出的加固墙体抗剪承载力计算公式与试验数据吻合较好,可在相关研究分析中参考使用。

不同填充墙构造方法对RC框架抗震性能影响研究

为定量评估不同填充墙构造方法对钢筋混凝土(reinforced concrete,RC)框架抗震性能的影响,搜集整理国内外砌体填充墙RC框架拟静力试验数据,筛选出19篇文献中共68个数据较为详尽的试件作为样本,分析对比柔性连接填充墙、增强填充墙整体性及设置阻尼耗能装置三类构造方法对试件的峰值点承载力、初始刚度、位移延性系数和等效黏滞阻尼系数4个参数的影响程度。结果表明:相较于传统构造方法,柔性连接填充墙框架的承载力和刚度均有所下降,变形能力提升;增强整体性的方法可提升试件承载力、刚度和变形能力,可作为一种较好的既有框架结构的加固方法;设置阻尼耗能装置虽然结构的承载力和刚度有所降低,但提升了结构的变形能力和耗能能力,在建造成本可接受的情况下可作为新建建筑的韧性提升方案。

纤维增强水泥基复合材料(ECC)面层加固砌体墙的压剪性能研究

为研究纤维增强水泥基复合材料(engineered cementitious composites,ECC)加固砌体结构后的压剪性能,对1片未加固砌体墙和6片ECC面层加固砌体墙进行了对角加载试验,分析了单、双面加固形式和面层厚度对墙体抗剪承载力的影响。进行了ECC加固砌体墙有限元模拟,与试验结果对比并进行参数分析。结果表明:ECC面层可显著提升砌体墙的抗剪承载力和变形性能,改善墙体的抗震性能;面层厚度、砂浆强度、ECC抗拉强度参数对墙体承载力影响显著,可为实际工程设计参数选取提供理论基础。提出了满足现有规范对墙体变形限值要求的ECC材料延伸率需求,以期为ECC加固砌体结构基于性能的抗震设计提供初步的理论支撑。

地震作用下冷库外围护砌体墙平面外动力响应规律研究

为探究冷库外围护砌体墙在地震作用下平面外动力响应规律,采用ABAQUS软件对3层冷库工程简化模型进行动力时程分析,分析平面外位移特征、平面外加速度及放大系数沿高度的分布规律,并对建筑抗震设计规范中等效侧力法的取值进行对比。结果表明:外围护墙在小震下未出现损伤,在中震下部分墙体中心出现损伤,在大震下墙体出现大面积损伤;外围护墙平面外动力响应受地面运动、主体结构层间位移、锚系梁刚度等因素影响,呈现出显著的动力放大效应;抗震设计规范中等效侧力法计算得到的冷库外围护砌体墙平面外地震作用偏小。为保证冷库的使用功能,工程设计中应采取提高冷库外围护砌体墙平面外抗震能力的措施。