Pseudo-dynamic tests on masonry residential buildings seismically retrofitted by precast steel reinforced concrete walls

A retrofitting technology using precast steel reinforced concrete（PSRC） panels is developed to improve the seismic performance of old masonry buildings. The PSRC panels are built up as an external PSRC wall system surrounding the existing masonry building. The PSRC walls are well connected to the existing masonry building, which provides enough confinement to effectively improve the ductility, strength, and stiffenss of old masonry structures. The PSRC panels are prefabricated in a factory, significantly reducing the situ work and associated construction time. To demonstrate the feasibility and mechanical effectivenss of the proposed retrofitting system, a full-scale five-story specimen was constructed. The retrofitting process was completed within five weeks with very limited indoor operation. The specimen was then tested in the lateral direction, which could potentially suffer sigifnicant damage in a large earthquake. The technical feasibility, construction workability, and seismic performance were thoroughly demonstrated by a full-scale specimen construction and pseudo-dynamic tests.

Twin lintel belt in steel for seismic strengthening of brick masonry buildings

A single-room,single-storey full-scale brick masonry building with precast RC roofing system was tested thrice under displacement controlled lateral cyclic loading,to assess the effectiveness of the basic repair and seismic strengthening techniques.Initially,the virgin building specimen was loaded laterally to f^tilure.In the second stage,the damaged building was repaired by stitching across the cracks,and tested under the same lateral loading.In the third stage,the twice-damaged structure was repaired once more by stitching and strengthened by twin lintel belt in steel and vertical comer reinforcement, and re-tested.The building strengthened by twin lintel belt in steel showed about 28% higher strength under lateral loading than the virgin building.

Seismic fragility reduction of an unreinforced masonry school building through retrofit using ferrocement overlay

The Himalayan region is one of the major seismic areas in the world.However,similar to many other seismically active locations,there are substantial numbers of unreinforced masonry(URM)buildings;the majority of which have not been designed for seismic loads.Past seismic events have shown that such buildings are highly vulnerable to earthquakes.Retrofitting of these URM buildings is an important concern in earthquake mitigation programs.Most government school buildings in rural areas of northern India are constructed of unreinforced masonry.These school buildings are socially important structures and serve as a crucial resource for rehabilitation during any disaster.The effectiveness of ferrocement(FC)to create a URM-FC composite is described in this study by estimating the performance and fragility of a URM school building before and after a retrofit.Analytical models,based on the equivalent frame method,are developed and used for nonlinear static analysis to estimate the enhancement in capacity.The capacity enhancement due to retrofitting is presented in terms of the maximum PGA sustained and damage probabilities at the expected level of earthquake hazard.

Observed failure modes of unreinforced masonry buildings during the 2015 Hindu Kush earthquake

On 26 th October 2015, an Mw 7.5 earthquake struck northern Pakistan, with its epicenter located 45 km southwest of Jarm in the Hindu Kush region of Afghanistan. The earthquake resulted from reverse faulting at a depth of 210 km, resulting in 280 fatalities and substantial damage to some 109,123 buildings. Regional seismicity, characteristics of recorded strong motions, damage statistics, and building performance observations are presented. Earthquake damage was mostly constrained to seismic-deficient unreinforced masonry(URM) buildings. Typical failure modes included toppled minarets, partial or complete out of plane collapse of URM walls, diagonal shear cracking in piers, flexural cracking in spandrels, corner damage, pounding damage, and damage due to ground settlement. The majority of human loss resulted due to failure of URM walls and subsequent roof collapse. URM buildings located in rural hilly areas closer to the epicenter suffered more intense and frequent damage than urban URM buildings located farther away in larger cities.

A 3-D DDA damage analysis of brick masonry buildings under the impact of boulders in mountainous areas

In mountainous areas, geological disasters carrying large boulders can cause severe damage to the widely used masonry buildings due to the high impact forces. To better understand the damage of brick masonry buildings under the impact of boulders, a "block-joint" model is developed using threedimensional discontinuous deformation analysis(3-D DDA) to simulate the behaviour of the "brick-mortar" structure. The "block-joint" model is used to capture not only the large displacement and deformation of individual bricks but also the large-scale sliding and opening along the mortar between the bricks. The linear elastic constitutive model is applied to account for the non-plastic deformation behaviour of brick materials. Furthermore, the mechanical characteristics of the mortar are represented using the Mohr-Coulomb and Drucker-Prager criteria. To propose safe structural design schemes and effective reinforcement for brick masonry buildings, seven construction techniques are considered, includingdifferent grades of brick and mortar, effective shear areas and reinforced members. The proposed 3-D DDA model is used to analyse the velocity distribution and the key point displacements of the brick masonry building under the impact of boulders. The results show that upgrading the brick and mortar, increasing the wall thickness, making full use of the wall thickness, and adding a circular beam and structural column are very effective approaches for improving the impact resistance of brick masonry buildings.

FUZZY MATHEMATICAL EVALUATION FOR MASONRY STRUCTURE BUILDINGS' DAMAGE GRADE CAUSED BY COAL MINING

Coal mining under buildings certainly causes surface movement and deformation, therefore, it brings about deformation even fracture for buildings. It is an important task to evaluate correcly the buildings’ damage grabe caused by coal mining. Fuzzy comprehensive evaluation,considering some factors of buildings’ fracture, has been applied to analyze the masonry structure buildings’ damage grade affer coal mining in this paper. It provides a scientific basis for buildings’reidercement before mining and maintenance or compensation after mining.

Analysis of the impact of large scale seismic retrofitting strategies through the application of a vulnerability-based approach on traditional masonry buildings

The buildings＇ capacity to maintain minimum structural safety levels during natural disasters, such as earthquakes, is recognisably one of the aspects that most influence urban resilience. Moreover, the public investment in risk mitigation strategies is fimdamental, not only to promote social and urban and resilience, but also to limit consequent material, human and environmental losses. Despite the growing awareness of this issue, there is still a vast number of traditional masonry buildings spread throughout many European old city centres that lacks of adequate seismic resistance, requiring therefore urgent retrofitting interventions in order to both reduce their seismic vulnerability and to cope with the increased seismic requirements of recent code standards. Thus, this paper aims at contributing to mitigate the social and economic impacts of earthquake damage scenarios through the development of vulnerability-based comparative analysis of some of the most popularretrofitting techniques applied after the 1998 Azores earthquake. The influence of each technique individually and globally studied resorting to a seismic vulnerability index methodology integrated into a GIS tool and damage and loss scenarios are constructed and critically discussed. Finally, the economic balance resulting from the implementation of that techniques are also examined.

Effect of vertical load difference on cracking behaviors in multistory masonry buildings and numerical simulation

To investigate the causes qf cracks in multistory masonry buildings, the effect of vertical load difference on cracking behaviors was investigated experimentally by testing and measuring the displacements at the testing points of a large sized real masonry U-shaped model. Additionally, the cracking behaviors in U-shaped model were analyzed with shear stress and numerical simulated with ANSYS software. The experimental results show that the deformation increases with the increase of the vertical load. The vertical load results in different deformation between the bearing wall and non-bearing wall, which leads to cracking on the non-beating wall. The rapid deformation happens at 160 kN and cracks occur firstly at the top section of non-bearing wall near to the bearing wall. New cracks are observed and the previous cracks are enlarged and developed with the increase of vertical load. The maximum crack opening reaches 12 mm, and the non-bearing wall is about to collapse when the vertical load arrives at 380 kN. Theoretical analysis indicates that the shear stress reaches the maximum value at the top section of the non-bearing wall, and thus cracks tend to happen at the top section of the non-bearing wall. Numerical simulation results about the cracking behaviors are in good agreement with experiments results.

Influence of Choice of Structural System &In-Fill Masonry on the Embodied Energy &Cost of a Low-Rise Residential Urban-Building Indian Case Study

In the urban residential building stock, a major proportion is constituted by low-rise individual buildings. In addition to cost, quality and duration, energy consumed for the project needs to be accounted in the decision making process. Minimizing the cost of construction without compromising on the architectural and structural requirements is the primary objective of the residential buildings of stake-holders, especially the owners. The choice of structural system and the materials used for construction play a crucial role in this effort. This means that the use of expensive and/or voluminous materials such as cement, steel, masonry etc. is optimized. This could lead to significant reduction in embodied energy as well, if the choice of the structural system is prudently made. In this paper, an attempt has been made to quantify the cost and embodied energy benefits for a low-rise residential building by choosing two different structural systems, namely moment resisting framed (MRF) construction system and the partly load-bearing (PLB) system. The influence of choice of materials, contributing to reduction of cost and/or energy is discussed. It is clearly noticed that, when the structural system is re-configured as a PLB system from the existing MRF system there is significant reduction in cost and embodied energy without changing the architectural form.

Seismic design analysis of the country masonry school buildings in the meizoseismal area

Several reinforcing schemes are illustrated that are based on the loading characteristics of typical country masonry school buildings with sparsely spaced transversal walls and large depth. From the seismic damage observed following the Wenchuan Earthquake, the effects of reinforcing schemes, tie-columns and tie-beams on the seismic resistance of masonry buildings are analyzed. The concept of improving the ductility of these types of buildings is presented. Finally, some suggestions are proposed for the design of masonry buildings with sparsely spaced transversal walls and large depth.

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.

Seismic Retrofit of Masonry Buildings with Polymer Grid

The performance of masonry walls reinforced using innovative polymer grids embedded into thin plaster layers as a tool for the seismic enhancement of brick masonry buildings has been investigated by experimental tests. A number of diagonal compression, shear compression and out-of-plane tests were executed on sample panels; experimental activities included pseudo-dynamic and shaking table tests on infills and reduced scaled building mock-ups, respectively. The results of the experimental activities are presented and discussed. Experimental campaigns have been supported by theoretical and numerical investigations; based on the experimental data and on the results of detailed numerical simulations, simplified models for the design of the retrofitting intervention are hereinafter proposed. The models：, calibrated on the experimental evidence, properly consider the collapse mechanisms as well as the grid effect in the evolution of the above mentioned mechanisms.

A comparison of IBC with 1997 UBC for modal response spectrum analysis in standard-occupancy buildings

This paper presents a comparison of the seismic forces generated from a Modal Response Spectrum Analysis （MRSA） by applying the provisions of two building codes, the 1997 Uniform Building Code （UBC） and the 2000-2009 International Building Code （IBC）, to the most common ordinary residential buildings of standard occupancy. Considering IBC as the state of the art benchmark code, the primary concern is the safety of buildings designed using the UBC as compared to those designed using the IBC. A sample of four buildings with different layouts and heights was used for this comparison. Each of these buildings was assumed to be located at four different geographical sample locations arbitrarily selected to represent various earthquake zones on a seismic map of the USA, and was subjected to code-compliant response spectrum analyses for all sample locations and for five different soil types at each location. Response spectrum analysis was performed using the ETABS software package. For all the cases investigated, the UBC was found to be significantly more conservative than the IBC. The UBC design response spectra have higher spectral accelerations, and as a result, the response spectrum analysis provided a much higher base shear and moment in the structural members as compared to the IBC. The conclusion is that ordinary office and residential buildings designed using UBC 1997 are considered to be overdesigned, and therefore they are quite safe even according to the IBC provisions.

Energy and Buildings

In 2011,the Danish government published an energy strategy for Denmark where one of the main targets are that Denmark should be a fossil-free society by 2050.Calculations show,that in order to reach this goal it is necessary to reduce the energy consumption of the existing building stock by 50 % on average.Since a 50 % reduction is obviously not possible for all buildings,those that can should aim for a so-called “deep energy renovation”,i.e.reducing the energy consumption to a level corresponding to that of new buildings or even more.This paper describes two case studies where multi-story apartment buildings have undergone deep energy renovation.“Traneparken” where the expected energy use after renovation aimed at a level corresponding to that of a new building according to the Danish Building Regulations from 2015.“Sems Have” where the aim was to go even further and meet the requirements expected for new buildings in 2020,i.e.corresponding to the Danish “nearly zero energy”-definition according to the EPBD.The paper reports on calculations and measurements of energy savings,the economy of the projects and looks at the added benefits or co-benefits that residents,housing association and society in general have achieved in addition to significant energy savings.

GPR Applications for NDT Investigations on the Cultural Heritage Monumental Buildings of Florence (Italy)

Florence (Italy) is a worldwide well-known cultural historical city, with many outstanding monumental buildings visited every year by about 20M people, since 1982 the historical city center is under the UNESCO Patronage. Conservation of monumental buildings is subject to the principles of integrity and authenticity, in Italy recalled by the Ministry for Cultural Heritage 2011 rule, which defines the procedure for their seismic vulnerability evaluation. For that, the knowledge of the masonry structure is in need, and in lack of historical documentation on the design, only non destructive tests (NDT), or very low destructive tests, can be run on the masonry for acquiring this knowledge on its structure and consistence. For this purpose, we are largely using specific ground penetrating radar (GPR) technology, which is resulting highly performing in defining masonry structure and consistence. This paper summarizes selected case histories regarding the main Florentine historical monumental buildings: Palazzo Vecchio, Brunelleschi’s Cupola, Giotto’s Bell-Tower, and San Giovanni Baptistery. The correct interpretation of the GPR data requires knowledge about the masonry techniques of the age of construction, and local verification with micro drill-holes with video inspections, sonic and ultrasonic tests, in defining historical monumental buildings masonry structure and competence, static and dynamic behavior parameters and seismic vulnerability.

Vibration transfer from underground train to multi-story building:Modelling and validation with in-situ test data

Excessive underground train-induced vibration becomes a serious environmental problem in cities.To investigate the vibration transfer from an underground train to a building nearby,an explicit-integration time-domain,three-dimensional finite element model is developed.The underground train,track,tunnel,soil layers and a typical multi-story building nearby are all fully coupled in this model.The complex geometries involving the track components and the building are all modelled in detail,which makes the simulation of vibration transfer more realistic from the underground train to the building.The model is validated with in-situ tests data and good agreements have been achieved between the numerical results and the experimental results both in time domain and frequency domain.The proposed model is applied to investigate the vibration transfer along the floors in the building and the influences of the soil stiffness on the vibration characteristics of the track-tunnel-soil-building system.It is found that the building vibration induced by an underground train is dominant at the frequency determined by the P2 resonance and influenced by the vibration modes of the building.The vertical vibration in the building decreases in a fluctuant pattern from the foundation to the top floor due to loss of high frequency contents and local modes.The vibration levels in different rooms at a same floor can be different due to the different local stiffness.A room with larger space thus smaller local stiffness usually has higher vibration level.Softer soil layers make the tunnel lining and the building have more low frequency vibration.The influence of the soil stiffness on the amplification scale along the floors of the building is found to be nonlinear and frequency-dependent,which needs to be further investigated.

Simplified seismic scenario analysis of existing masonry buildings accounting for local site effects

This study discusses the effects of local sites and hazard amplification on the seismic vulnerability assessment of existing masonry buildings.In this context,a rapid seismic evaluation procedure was implemented on an old masonry building stock in the historical center Galata,located inİstanbul,to determine the seismic risk priority of the built heritage.Damage scenarios were generated for all soil classes,different moment magnitudes,and source-to-site distances to obtain more accurate results for the seismic vulnerability assessment of the studied building stock.Consequently,damage distributions estimated under nine different scenarios with/without site effects were compared and illustrated in maps to discuss changes in vulnerability owing to amplification effects.In this study,by re-examining the rapid seismic evaluation procedure by including geo-hazard-based assessment,the importance of site effects on the vulnerability and risk assessment of built heritage was underlined.The proposed framework integrating field data and local site effects is believed to advance the current applications for vulnerability assessment of masonry buildings and provide an improvement in the application of rapid seismic assessment procedures with more reliable results.

Experimental Investigation of Bed Joint Reinforcement Corrosion in Masonry Mortars

The paper investigates the behaviour against corrosion offered by seven masonry mortar compositions to the reinforcement placed in masonry bed joints. Durability protection was evaluated on the basis of four criteria: carbonation area of the specimens, mass loss of steel, electrochemical potential and presence of chloride ions. Tests were performed against two corrosive environments, with and without chloride ions, and were carried out for three periods: three, six and thirty three months. Two types of steel were used, plain steel and galvanized steel. Moreover, the steel protective action of a corrosion inhibitor, sodium nitrite, was examined. A qualitative comparison approach against prototype concrete-like mortars was used. The results showed that the selected masonry mortars did not exhibit similar properties against corrosion to those of concrete and that the addition of sodium nitrite decrease of the corrosion rate only 5% - 20% did not meaningfully improve durability properties. Nevertheless, the addition of lime in small quantities did not have a negative impact on the mortars’ durability characteristics, e.g. the same average corrosion rate.

装配式配筋砌块砌体结构技术与应用

当前在国家大力倡导建筑业采用装配化建造方式的背景下,装配式混凝土结构、装配式钢结构等建筑新技术不断涌现并在工程建设中大量应用,而砌体建筑在这次装配化建造大潮中比较沉寂。砌体结构领域的工作者一直也在积极探索,介绍了砌体结构中一种配筋砌块砌体结构实现装配化建造的技术,该技术先以标准化生产的砌块产品组装成个性化需求的墙构件,再将墙构件经绑扎后在施工现场吊装并在安装中穿入竖向钢筋,最后用混凝土灌孔连接形成整体结构。该技术是基于理论试验研究及工程实践验证后得出的新成果,已有近20万m^(2)规模的工程实践应用,具有成本低、工艺简、安全性好、效率高等特点,为采用装配化方法建造房屋提供了新的选择。

泸定6.8级地震城镇居住建筑典型震害及启示

为分析泸定68级地震中城镇居住建筑的破坏情况,对位于震中磨西镇及周边城镇居住建筑的典型震害进行调查,总结了城镇居住建筑中框架结构及砌体结构的震害特征,详细介绍了一栋采用框架结构的高层住宅及一栋采用砌体结构的多层员工宿舍的破坏情况,并分析破坏原因。调查与分析结果表明:本次地震中,框架结构和砌体结构破坏普遍在底层更严重;框架结构震害总体较轻,未合理设计的楼梯及填充墙依然是框架结构中震害集中区;砌体结构墙体出现常见的各种斜向裂缝;除设计因素外,造成少量砌体结构倒塌可能原因是传统砌体结构抵抗竖向地震作用能力不足以及特殊场地地震放大效应。根据两种结构类型的建筑震害特征,对灾区重建及既有房屋改造提出了重点加强老旧建筑合规性排查、合理计算不利地段建筑的地震作用、适当引入合适的减隔震装置等针对性的设计建议,以提高城镇居住建筑的抗震能力,同时体现韧性城镇的设计理念。