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 D max(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

这份报纸为石工技术包围和填入墙讨论表演要求和构造标准的问题。在欧洲国家的垂直大楼围场被 non-load-bearing 石工技术墙很经常组成，用水平地穿孔的泥土砖。这些墙被柱和横梁 / 平板的增强的具体框架结构通常支持并且限制。因为这些墙通常被认为是 nonstructural 元素，他们对结构的反应的影响被忽略，他们在象他们到邻近的结构的元素的连接一样的结构的设计的考虑经常玩忽或不足地详细说明。作为后果，至于墙围场，当大楼受到地震行动时， nonstructural 元素对飘移和加速要求相对敏感。许多国际标准和技术文件为 nonstructural 元素为设计可接受程度标准强调需要，然而，他们明确地不显示怎么阻止倒塌并且严重裂开，并且怎么在情况中提高全面稳定性对高地震的装载中等。而且，适当措施的评论被探讨在地震行动下面改进包围墙性能和在里面飞机和 out-of-plane 正直。

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.

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.

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.

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 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 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。

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。

Experimental investigation of engineered geopolymer composite for structural strengthening against blast loads

The recent increase in blast/bombing incidents all over the world has pushed the development of effective strengthening approaches to enhance the blast resistance of existing civil infrastructures.Engineered geopolymer composite(EGC)is a promising material featured by eco-friendly,fast-setting and strain-hardening characteristics for emergent strengthening and construction.However,the fiber optimization for preparing EGC and its protective effect on structural elements under blast scenarios are uncertain.In this study,laboratory tests were firstly conducted to evaluate the effects of fiber types on the properties of EGC in terms of workability,dry shrinkage,and mechanical properties in compression,tension and flexure.The experimental results showed that EGC containing PE fiber exhibited suitable workability,acceptable dry shrinkage and superior mechanical properties compared with other types of fibers.After that,a series of field tests were carried out to evaluate the effectiveness of EGC retrofitting layer on the enhancement of blast performance of typical elements.The tests include autoclaved aerated concrete(AAC)masonry walls subjected to vented gas explosion,reinforced AAC panels subjected to TNT explosion and plain concrete slabs subjected to contact explosion.It was found that EGC could effectively enhance the blast resistance of structural elements in different scenarios.For AAC masonry walls and panels,with the existence of EGC,the integrity of specimens could be maintained,and their deflections and damage were significantly reduced.For plain concrete slabs,the EGC overlay could reduce the diameter and depth of the crater and spallation of specimens.

矿山用智能砌墙机的设计与研究

分析了当前矿山开采中,采用人工砌筑巷道挡墙的现状及弊端,根据井下巷道类型和挡墙形态,自主研发了一种适应井下巷道等受限空间工作环境的、自动化程度高、能砌筑多种挡墙类型的智能砌墙机,并对该设备的主要部件及功能以及工作流程进行了详细分析。实践证明,该设备可以大幅降低工人劳动强度,减少现场作业人工数量,提高砌筑效率,进而降低施工成本,提高挡墙砌筑机械化、自动化程度,提高矿山作业安全性。

气候变化背景下内保温砖墙热湿性能对比

为量化气候变化背景下内保温砖墙的热湿性能,采用数值模拟软件WUFI Pro,对比湿气密闭性保温墙体、湿气透过性内保温墙体和未保温墙体,分析其在比利时鲁汶1种现状气候工况和2种未来气候工况下的冻融循环风险、霉菌滋生风险、热损失和湿负荷.结果表明,湿气透过性保温墙体与湿气密闭性保温墙体的冻融风险次数由现状气候工况下的6和2次升至未来气候工况下的16和13次,且含水率显著增高,而未保温墙体无风险.湿气密闭性保温墙体在3种工况下的霉菌滋生风险都显著高于其余2种墙体,且在未来气候工况下风险更高.含保温层墙体的能耗显著低于未保温墙体,湿气透过性保温墙体与未保温墙体在未来气候工况下需要更大的湿负荷.

装配式砌体墙片抗冲击性能试验研究

装配式砌体墙片在运输、安装及使用过程中,易受到人力或者施工机械的冲击,可能产生较大的变形或破坏。为研究装配式砌体墙片在运输、安装及使用时的抗冲击性能,采用摆锤法对仅设水平灰缝的装配式自动码垛砌体墙片和传统人工砌筑的墙片进行冲击试验,测试分析了在外冲击荷载作用下墙片的位移变化特征、开裂情况和破坏形式。试验结果表明:仅设水平灰缝的装配式砌体墙片横向和竖向位移均大于传统码垛工艺砌筑的墙片;在墙片受冲击时,缺少竖向灰缝约束的墙体整体稳定性降低,结构平面外冲击荷载对墙体的影响较大。两组墙体经10次冲击后产生裂缝,裂缝由上往下发展;15次冲击后出现结构性破坏但满足规范中墙片抗冲击性能符合规范要求,可满足实际工程需要。