Learning from Construction Failures due to the 2009 L’Aquila, Italy, Earthquake

An earthquake sequence struck the province of L’Aquila (central Italy) leaving 305 dead, about 1,500 injured, and 29,000 homeless. Hundreds of low-intensity events occurred between January and March, 2009. The mainshock took place on April 6, 2009, and its epicenter was located at about 6 km southwest of L’Aquila town; three stronger aftershocks happened on April 7 and 9, 2009. This paper focuses on actual performance of older and more recently constructed building structures during the earthquake sequence. After the main seismological characteristics of the sequence are described, the most significant observed damages are analyzed and associated with theoretical failure modes for both reinforced concrete and unreinforced masonry buildings. Since older masonry structures were more seriously damaged, the effects of the earthquake are described with more emphasis to ordinary masonry and cultural heritage buildings (churches, palaces, and castles). In conclusion, a number of lessons may be learned from the L’Aquila earthquake sequence. Several features are highlighted and some proposals are given to upgrade the current methods of structural analysis, as well as the existing codes.     

Evaluation of Strengthening Techniques of Traditional Masonry Buildings: Case Study of a Four-Building Aggregate

Increasing appraisal of the durability, conservation state, and changeable use and function of old buildings in urban centers relies a great deal on the structural safety evaluation of vertical load capacity and the ability to resist horizontal forces. The need to assess seismic vulnerability, particularly of traditional masonry buildings, is a key issue. Evaluation of the seismic vulnerability of old buildings is essential in the definition of strengthening needs and minimization of damage from seismic actions in the safeguarding of built heritage. A three-dimensional model was developed for an aggregate of four traditional masonry buildings located in the old city center of Coimbra, in Portugal. The finite element modeling of these buildings has aimed to identify structural fragility, understand the damages detected, and evaluate the global structural safety of these types of buildings. The primary results obtained in this case study helped to interpret the structural damage and stress distribution, and verified global stability and its consequences. Different strengthening techniques to improve the global behavior of these buildings were modeled and analyzed. A comparison of the efficiencies of strengthening strategies is also discussed.     

Performance of Masonry Stone Buildings during the March 25 and 28, 2004 A?kale (Erzurum) Earthquakes in Turkey

This paper reviews the performance of stone masonry buildings during the March 25 and 28, 2004, A?kale (Erzurum) earthquakes. A?kale is a township located 35?km from Erzurum city in Turkey. A majority of the buildings in the affected region are built in masonry. Most of the masonry buildings were formed with random or coursed stone walls without any reinforcement supporting heavy clay tile roofing over wooden logs. A large number of such buildings were heavily damaged or collapsed. The cracking and failure patterns of the buildings are examined and interpreted relative to current provisions for earthquake resistance of masonry structures. The damages are due to several reasons such as site effect, location, and length of the fault, and the poor construction quality of the buildings. In addition to these reasons, the two earthquakes hit the buildings within three days, causing progressive damage. Low strength stone masonry buildings with mud mortar are weak against earthquakes, and should be avoided in high seismic zones.     

Evaluation of Building Stiffness for Building Response Analysis to Excavation-Induced Ground Movements

A major element in the design and construction of tunnels and braced excavations in urban areas is the control of ground movements and protection of adjacent or overlying structures, which are often constructed with masonry and set on shallow foundations. Initial evaluation of potential building damage is obtained by assuming that building distortion is compliant with the imposed ground movements. Further investigations take into consideration the reduction in building distortion that occurs as a result of building stiffness. Presented in this paper are the results of numerical analyses for evaluating the equivalent bending and shear stiffness of masonry structures taking into account the anisotropy of the masonry units and the percentage of window openings. The distinct element code, UDEC, has been used to model each masonry block and the mortar between blocks for masonry walls in plane stress conditions. Parametric studies, conducted for a range of window opening percentage and brick/mortar joint stiffness, show that the equivalent shear stiffness for buildings with windows are low, typically in the range of 1/10–1/20 of the equivalent bending stiffness. Thus, for most masonry buildings, the shear deformation is dominant for a building subjected to excavation-induced ground movements. Equivalent bending and shear stiffness evaluated by the numerical analyses is compared with field data and analytical calculations, which may be available only for the case of no window openings.     

Design Guidelines for Community Shelters for Extreme Wind Events

The design of shelter structures has received little attention from the engineering community since the days of nuclear fallout shelters, until the development of guidance for community shelters for cases of extreme wind events was released by FEMA in July 2000 (FEMA 361). To respond to the recent demand for community shelters, many states are designating existing schools or other public buildings, such as community centers or multipurpose buildings, as public shelter areas. In most cases these buildings, or portions of these buildings, were never designed for use as shelters. Most of the designated shelters were designed and constructed according to older local building codes that do not include requirements for extreme wind pressures and uplift. Even recently designed structures have been found to have inadequate features for a high-wind shelter, particularly with respect to cladding and architectural features that are vulnerable to damage from high winds and windborne debris. Damage to the cladding is often the beginning of building failure and occupant injury during an extreme wind event. This paper identifies critical issues and gaps in presently available technology for evaluating proposed shelters and providing retrofit guidance to building owners. The writers’ experience with inspections of designated shelters, proposed retrofit recommendations, and damage investigations of buildings affected by hurricanes or tornadoes is summarized. Recommendations for design considerations that include the current standards of practice as outlined in FEMA 361, ASCE 7-98, and the Florida Shelter Evaluation Guidelines are given.     

砖混住宅顶层墙体裂缝的受力分析与防治

文章对砖混结构墙体裂缝向题进行了温度应力、地基不均匀沉降、砌体温度、变形等若干项分析,并针对墙体裂缝提出有效的防治措施。     

Retrofitting Existing Masonry Buildings to Resist Explosions

In recent years, many buildings around the world have had their windows protected or strengthened to resist the effects of explosions in an attempt to reduce the level of casualties associated with terrorist bomb attacks. While the windows form the most vulnerable parts of a building, occasionally it becomes necessary to strengthen the walls as well—particularly in older and weaker historical structures or where the blast loads are high. This paper highlights a number of different techniques available to the structural engineer and security specialist that can be employed to make existing masonry walls stronger and more capable of safely resisting the effects of explosions.     

Dynamic Testing of a Masonry Structure on a Passive Isolation System

Lightly reinforced and unreinforced masonry buildings have not performed well in earthquakes. Evaluation of past performance of masonry structures has led to more stringent design and construction requirements in the current building codes, and has raised concerns about the performance of existing lightly reinforced and unreinforced masonry buildings in future earthquakes. Base isolation has been shown to be effective in reducing damage to large building structures, and appears to be particularly effective in protecting stiff masonry structures. Using the base isolation principle, Kansas State University’s stiffness decoupler for the base isolation of structures (SDBIS) was designed to effectively reduce the acceleration and force transferred into a building superstructure during a seismic event. The sliding system uses a passive method to provide damping and to dissipate some of the kinetic energy to reduce relative displacements. In addition, the SDBIS system includes a self-centering element that will recover the majority of the induced displacement and provide resistance to overturning. In order to apply the SDBIS system to the masonry building industry, dynamic testes were performed to evaluate the structural response of a full-size one-story masonry model that was supported by the SDBIS system. Acceleration time-history results are presented for dynamic tests using the July 21, 1952 Kern County earthquake, Station 1095 Taft Lincoln School record, the May 19, 1940 Imperial Valley earthquake, Station 117 El Centro Array #9 record, the February 9, 1971 San Fernando earthquake, Station 279 Pacoima Dam record, and the January 17, 1994 Northridge earthquake, Station 24436 Tarzana Cedar Hill record ground motions. Test results show the system is effective when used with a masonry structure.     

Experimental In-Plane Behavior of Tuff Masonry Strengthened with Cementitious Matrix–Grid Composites

Tuff buildings are a significant part of the Mediterranean area and are to be preserved from a structural viewpoint especially in seismic areas. Over the past few decades, the interest in strengthening of historical tuff masonry structures has led to developing specific and noninvasive architectural and engineering strategies. In the present paper, a comprehensive experimental program on tuff masonry panels is presented; the results are intended as a contribution to the knowledge of in-plane behavior of tuff masonry strengthened with composite materials. Particularly, a cement based matrix-coated alkali resistant glass grid system (CMG) was used to strengthen tuff masonry walls; different CMG layouts were selected, and overall performances were compared with those of as-built ones. The characterization of base materials was carried out first, followed by uniaxial tests of masonry and shear tests on triplets. Finally, tuff masonry panels were subjected to diagonal compression loading under displacement control in order to measure their in-plane deformation and strength properties, including the postpeak softening regime in view of seismic applications.     

Experimental Response of Externally Retrofitted Masonry Walls Subjected to Shear Loading

Recent earthquakes have produced extensive damage in a large number of existing masonry buildings, demonstrating the need for retrofitting masonry structures. Externally bonded carbon fiber is a retrofitting technique that has been used to increase the strength of reinforced concrete elements. Sixteen full-scale shear dominant clay brick masonry walls, six with wire-steel shear reinforcement, were retrofitted with two configurations of externally bonded carbon fiber strips and subjected to shear loading. The results of the experimental program showed that the strength of the walls could be increased 13–84%, whereas, their displacement capacity increased 51–146%. This paper presents an analysis of the experimental results and simple equations to estimate the cracking load and the maximum shear strength of clay brick masonry walls, retrofitted with carbon fiber.     

FRP Confinement of Square Masonry Columns

The problem of masonry columns subjected to structural deficiency under axial load was studied and reported in this paper. The results of an extensive experimental campaign are presented in order to show the behavior of columns built with clay or with calcareous blocks, commonly found in southern Italy, especially in historical buildings. Rectangular masonry columns were tested for a total of 33 specimens; uniaxial compression tests were conducted on columns taking into account the influence of several variables: different strengthening schemes (internal and/or external confinement), curvature radius of the corners, amount of fiber-reinforced polymer (FRP) reinforcement, cross-section aspect ratio, and material of masonry blocks. Materials characterization was preliminarily carried out including a mechanical test on plain masonry. For all cases the experimental results evidenced a significant increase in load carrying capacity and ductility after FRP strengthening, which identified the columns as ductile elements despite the brittle nature of the unconfined masonry. Differences in mechanical behavior, due to the geometry of the columns, to the nature of different materials, to different strengthening schemes, and to the amount of reinforcement, are presented and discussed in the paper. The calibration of design equations recently developed by Italian National Research Council, CNR was conducted to compare analytical prediction and experimental results. The same procedure was applied to calibrate an analytical model recently published, in which the existing coefficients are related only to clay. Here the model is applied to limestone for the first time. Thus, new important information is furnished to researchers and practitioners involved in structural assessment and strengthening of compressed elements in historical buildings.     

Rehabilitation of Masonry Walls Using Unobtrusive FRP Techniques for Enhanced Out-of-Plane Seismic Resistance

Earthquake damage to unreinforced masonry buildings has shown the vulnerability of perimeter walls to out-of-plane failure. This paper describes a study that was carried out to develop and test innovative fiber reinforced polymer (FRP) rehabilitation techniques that meet the stringent requirements for strengthening historical buildings and to be cost-effective alternatives applicable to other existing masonry structures. Unobtrusive FRP rehabilitation techniques that utilize flexible carbon fiber composite cables, mounted near the surface of the fa?ade walls in epoxy-filled grooves in the bed and head joints, were developed. Ten full size walls were constructed of clay bricks and retrofitted using the developed FRP rehabilitation techniques. The test results demonstrated the high efficiency of the rehabilitation techniques under both monotonic and quasistatic cyclic loadings. Significant increases in ultimate capacities, energy absorption, and deformability were achieved for various reinforcing schemes compared to the behavior of the unreinforced walls.     

江西省科技馆展览及综合楼空调设计

针对顶部与东西两侧建筑维护结构材料为玻璃的高大空间-阳光咖啡厅，空调采用了分层空调的方式，节省能源同时保证空调使用效果。     

Building Robustness Research during World War II

This study reviews research carried out in the U.K. to understand and improve the robustness of buildings when subject to blast from high explosive bombs. The work concentrates on the performance of ordinary civilian buildings, with particular emphasis on multistory buildings framed in either reinforced concrete or structural steelwork. At that time, some of the data were used to enhance conventional building construction, principally on government buildings, and some were used to aid postwar hardened building construction. The two main U.K. researchers whose work is the basis of this paper (Professor Sir Dermot Christopherson and Professor Lord Baker) identified a number of building weaknesses that led to local or progressive collapse, including connections in steel-framed buildings, as well as detailing weaknesses in reinforced concrete constructions. This paper reviews these features, as well as those that added resilience to bomb damage, with particular emphasis to the use of masonry infill panels in framed buildings. Much of the information on building performance is relevant to today’s engineers engaged in the design of buildings to survive blast from terrorist attacks involving a vehicle-borne improvised explosive device.     

Nondestructive Testing Evaluation of Drying Process in Flooded Full-Scale Masonry Walls

After an investigation on the most recent floods occurred in Italy that damaged the Cultural Heritage masonry buildings, an experimental research started on-site on full-scale masonry models exposed to the environmental agents in Milan. The masonry materials used for the full-scale models were largely investigated in the past and the models were subjected to decay caused by the capillary rise and by the crystallization of sodium sulfate coming from the foundations. These walls can actually simulate the state of naturally contaminated walls before a flood and represent a construction where the main parameters are known. A flood has been simulated by adding water for several days to the walls of the full-scale models previously contaminated by salts, then the walls were left to naturally dry. The objective is to check the effectiveness of nondestructive (ND) techniques in detecting the presence of water and the drying process and also the influence of surface treatments presence. Radar tests, thermography tests, sonic tests, as well as the minor destructive powder drilling tests were applied successfully to evaluate the moisture distribution in the masonry after flooding and during natural drying.     

Masonry Confinement with Fiber-Reinforced Polymers

The application of fiber-reinforced polymer (FRP) as a means of increasing the axial capacity of masonry through confinement, a subject not addressed before, is investigated in this study. Four series of uniaxial compression tests, with a total of 42 specimens, were conducted on model masonry columns with these variables: number of layers, radius at the corners, cross-section aspect ratio, and type of fibers. It is concluded that, in general, FRP-confined masonry behaves very much like FRP-confined concrete. Confinement increases both the load-carrying capacity and the deformability of masonry almost linearly with the average confining stress. The uniaxial compression test results enabled the development of a simple confinement model for strength and ultimate strain of FRP-confined masonry. This model is consistent with the test results obtained here but should attract further experimental verification in the future to account for types of masonry materials other than those used in this study.     

Structural Upgrading of Masonry Columns by Using Composite Reinforcements

Emerging techniques that use fiber-reinforced polymer (FRP) composites for strengthening and conservation of historic masonry are becoming increasingly accepted. In the last decades steel plates or wood frames were used for external confinement in containing the lateral dilation of masonry columns subjected to axial loads. In the last years FRP epoxy bonded strips or jackets were also employed to increase strength and ductility with encouraging results in terms of mechanical behavior and cost effectiveness. The behavior of masonry columns confined with FRP and subjected to axial compression is studied in this paper. An extended experimental investigation is presented in order to show the mechanical behavior of circular masonry columns built with calcareous blocks that may be commonly found in Italy and all over Europe in historical buildings. Different stacking schemes were used to build the columns, aiming to simulate the most common situations in existing masonry structures. Carbon FRP sheets were applied as external reinforcement; different amounts and different schemes of confining reinforcement were studied. The experiments include a new reinforcement technique made by using injected FRP bars through the columns cross section. Such a solution can be considered in place of a more traditional confinement, when external reinforcement must be avoided, or in addition to external reinforcement when an improved confinement effect is required. The structural behavior of masonry columns damaged under different levels of load and strengthened by using FRP reinforcements, was also investigated. Experimental results revealed the effectiveness of the FRP confinement for masonry columns, also for columns that were strongly predamaged before strengthening. A computation of the ultimate load was conducted using the Italian National Research Council recommendations to show an application of the design approach recently proposed in Italy. An existing analytical model, previously developed by the writers, was applied for computation of expected experimental values.     

Investigation and Repair of Structural Deficiencies in Projected Masonry Bay Construction

Projected masonry bays are a common feature on many historic buildings. Over the course of the last 100?years or so, bays have been constructed utilizing a wide variety of masonry and framing configurations to provide structural support to these eccentric architectural elements. Mechanisms to resist the natural tendency of the bay construction to “sag” and/or rotate away from the plane of the wall have historically included corbelled and/or cantilevered masonry, steel tension ties, counterweight beams, and a variety of steel, concrete, and wood framing configurations. Many of these support system mechanisms have satisfactory in-service performance, whereas others have been found to permit undesirable behavior. Unanticipated flexibility in the bay support may result from improper interaction of the various structural components. Distortion of the bay construction leads to distress, premature deterioration, and sometimes failure within the bay assemblies. This paper will present a case study pertaining to the investigation, analysis, and repair of a projected masonry bay system involving several different support mechanisms and will focus on a specific structure in which effective support assemblies were integrated into the existing building fabric.     

Masonry Wall Crack Control with Carbon Fiber Reinforced Polymer

Restrained shrinkage is a major source of damage to buildings. By the combination of different construction materials, or through different conditions of exposure of different structural elements, differential dimensional change occurs. Thereby, stresses arise, which can cause cracking. In recent combined experimental and numerical research projects, this source of damage to masonry walls has been confirmed. The ability has been developed to predict the level of damage computationally. This paper addresses a method to reduce the width of cracks in masonry walls subjected to restrained shrinkage, to acceptable levels. Crack control by externally applied carbon fiber reinforced polymer (CFRP) reinforcement is studied. Although structural strengthening by CFRP reinforcement is actively researched, its application here to preserve structural serviceability is novel. An experiment was designed and performed to study the response of an unreinforced masonry wall to restrained shrinkage. Subsequently, the wall was repaired and reinforced on one face with CFRP strips. The required CFRP reinforcement was designed by finite element analysis, which also served as prediction of the response of the reinforced wall to restrained shrinkage.     

Investigation of Seismic Behavior and Infill Wall Effects for Prefabricated Industrial Buildings in Turkey

Recently, Turkey has been hit by several moderate to large earthquakes that resulted in significant loss of life and property. The 1998 Adana and 1999 Marmara earthquakes caused severe damage not only in residential buildings but also in industrial buildings. Most of the industrial buildings in Turkey are constructed as prefabricated structures. Prefabricated structures are preferred because of their economic and rapid production. In the present study, the earthquake behavior and infill wall effects for single story hinged industrial prefabricated buildings were investigated. Nonlinear pushover, performance-based, time history, and fragility analyses were carried out for a sample prefabricated industrial building. Infill wall effect was investigated by adopting a diagonal strut model. The structural behavior and load-deformation relationship of prefabricated industrial buildings both with and without infilled walls were evaluated and compared. Results of the study show that masonry infill walls can affect the lateral load-carrying capacity and modify the earthquake response of prefabricated industrial buildings.