The Baseline Stiffness Method for Damage Detection in Buildings Without Baseline Modal Parameters

A new method called the Baseline Stiffness Method (BSM), used to locate and quantify damage in buildings without baseline modal parameters (undamaged state), is presented. In order to determine this reference state, the BSM uses modal parameters from the damaged state of the building and the lateral stiffness matrix of the first story without damage. Afterwards, by means of an iterative process using singular value decomposition, location and severity of damage are obtained by comparing information about the damaged and non damaged states. Numerical and experimental examples are presented and discussed showing the advantages of the application of the proposed BSM.     

Shaking Table Testing of a Full-Scale Prefabricated Three-Story Timber-Frame Building

Shake table tests were carried out on a 7 m × 5 m three-story, timber light-frame building (7.5 m height) at the TreesLab laboratory (Eucentre) in Pavia. The aim of the research was to evaluate the seismic behavior of a typical Italian prefabricated timber building and to study the interaction between the individual structural components tested in quasi-static manner in a previous experimental study. The 1979 Montenegro Earthquake ground motion, recorded at the Ulcinj-Hotel Albatros station, was selected as the ground motion for seismic tests. The maximum peak ground acceleration was scaled to 0.07 g, 0.27 g, 0.5 g. 0.7 g, and 1 g in order to evaluate the building’s performance at different levels of seismic input. More than 100 instruments were used to monitor the behavior of the building during seismic tests measuring acceleration, displacement, and forces. The visual inspection shows that the building did not show any damage during all seismic tests. However the data analysis (dynamic identification, capacity spectrum, inter-story drift) confirm that during the 1.00 g test the structure went beyond its linear elastic limit. The results obtained from this experimental study suggest that the design hypotheses commonly adopted in practice for seismic analysis (e.g., in terms of force distributions between the walls, and also the behavior factor q) are not always consistent with the real behavior of timber frame multi-story buildings, and should be backed by more accurate knowledge of the contributions of the individual structural components.     

Performance of Structures in the Mw 6.1 Mae Lao Earthquake in Thailand on May 5, 2014 and Implications for Future Construction

An M_w 6.1 earthquake struck northern Thailand on the 5^th of May 2014. The epicenter was located near Mae Lao district in Chiang Rai province. The earthquake caused unprecedented damage to structures, the most damaging earthquake ever in recorded Thai history. Five hundred and ninety-four buildings out of 10,863 were damaged to the extent that they were unsafe for occupancy. This article presents a reconnaissance investigation of damage to buildings and bridges in the two districts—Phan and Mae Lao—which suffered the most damage. Attention is paid to the performance of buildings with similar configurations and structural design, but with different layout of unreinforced masonry infills as non-structural components.     

Seismic Response of a Four-Story Miniature Building with Replaceable Plastic Hinges

To emphasize on linear and nonlinear seismic behavior of building systems in education, a four-story miniature moment-resisting frame steel building was designed, built, and tested in a shaking table at the Structures Laboratory of the Department of Civil Engineering at the University of Canterbury, New Zealand. A prominent feature of the building is the incorporation of elements designed to form plastic hinges that can be easily replaced after a test with minimum effort and at a very low cost. This model is mainly aimed at education in undergraduate and graduate structural dynamics/earthquake engineering courses and it has also been used to support research. This article describes in detail the main features of the building, its design, and discusses the response of the building to two input ground motions. Because the use of pushover analyses is becoming an industry standard, the some relevant results will be compared with those predicted by such kind of analyses. This article is written in very simple terms and is aimed at the undergraduate and graduate student, at educators in structural design and at structural engineers involved in seismic design of building structures. This article covers many aspects that are seldom highlighted in building behavior to earthquake excitation and that are not always covered in design codes or guidelines.     

The Courage of their Convictions: Creating Cultural Landscapes in 1930s Western Australia

Building a cultural landscape involves deep political and social processes. Discussions relating to decisions about preservation reveal cultural values at a particular moment and explain the character of the surviving landscape. This study analyses how one community in Western Australia defined its sense of place and identity. In the 1930s, on a wave of historical consciousness, Western Australians sought to enshrine the desire to preserve a range of historical materials in legislation, and conducted debates about the very survival of the buildings and documents. This paper investigates why legislation to preserve buildings and documents failed, and how the community understood the relationship between these two forms of heritage. Bringing together the two series of discussions, about the values inherent in and surrounding documents and buildings, highlights the way in which meanings are invested in places and things, and the values and processes through which the cultural landscape is shaped.     

Book Reviews

Over the past 150 years, different perceptions concerning the cultural influence that historic buildings should exert on modern life have evolved within the British Isles and Continental (especially Central) Europe. Despite a conservation revival, together with the declining influence of International Modernism by the 1970s, in facilitating the reduction of conceptual differences within state conservation agencies throughout Europe, subsequent events did not allow this process to go much further. The political changes in Central Europe following the end of the Cold War and the subsequent restructuring of the world economy helped to re-emphasise the basic problem. That is, the extent to which the material remains of the past should be considered more as reactive cultural icons or more as proactive normative elements within the European civic tradition. An examination of the general operating philosophies of state conservation agencies in England and Germany can give a plausible insight into how differing values placed on the past and contemporary significance of historic buildings can be directly related to the level of vernacular continuity deemed appropriate within different European regions. The question is also raised whether the convergence of similar urban lifestyles across the European Continent will enable historic material remains to become either integrated and moral realities or hermetic and virtual realities within the broader framework of European civic life.     

Sensitivity of the Earthquake Response of Tall Steel Moment Frame Buildings to Ground Motion Features

The seismic response of two tall steel moment frame buildings and their variants is explored through parametric nonlinear analysis using idealized sawtooth-like ground velocity waveforms, with a characteristic period (T), amplitude (peak ground velocity, PGV), and duration (number of cycles, N). Collapse-level response is induced only by long-period, moderate to large PGV ground excitation. This agrees well with a simple energy balance analysis. The collapse initiation regime expands to lower ground motion periods and amplitudes with increasing number of ground motion cycles.     

Numerical Analysis of RC Bridge Piers with Rectangular Hollow Cross-section Retrofitted with FRP Jackets

The research presented in this article deals with the seismic retrofit of bridge piers with rectangular hollow cross-section using fiber-reinforced polymer (FRP) jackets. A two-level numerical approach that combines finite element method (FEM) analyses and fiber modeling is proposed. The FEM is used to study the effect of FRP jackets on the properties of concrete. The analyses show that the existing empirical laws for FRP-confined concrete are not suitable for piers with hollow cross-section, as the effect of confinement is not uniform within the cross-section and the stress–strain curves show softening after peak strength. Fiber modeling is used to study the global behavior of reinforced concrete piers with rectangular hollow cross-section wrapped with FRP jackets. To account for confinement, the properties of the concrete fibers are modified according to the results of the FEM analyses. The proposed method is validated against experimental results and used for an extensive parametric study. It is found that the effectiveness of jacketing is conditioned by the axial load, longitudinal reinforcement, and jacket dimensions. An empirical design equation is formulated on the basis of the numerical analyses.     

Modeling the Cyclic Flexural and Shear Response of the R. C. Hollow Box Columns of an Existing Viaduct

The cyclic response of R.C. hollow box columns, constructed as part of a typical single-column bent viaduct, built in the 1970’s in Central Europe, was studied both experimentally and analytically. Moderate displacement ductility capacity (between 3 and 4) was observed regardless of the column construction details, which are nowadays considered inappropriate for seismic regions. Standard analytical flexural models correlated with the experimental results quite well. Shear strength was estimated using the two methods included in the EC8 standards, as well as the method developed at the University of California, San Diego. Quite different results were obtained. The most accurate was the third method.     

Distribution of Lateral Forces in Base-Isolated Buildings Considering Isolation System Nonlinearity

The ASCE 7 equivalent lateral force method for base-isolated buildings applies a triangular distribution of forces to the superstructure. This distribution attempts to approximately account for the observed effects of isolation system nonlinearity on the superstructure response, but a more rational approximation is needed. Using nonlinear regression analysis of median response data from nonlinear response history analysis of representative systems, improved equations are developed to estimate the lateral force distribution in the superstructure. The ASCE 7 distribution, a revision considered by a SEAONC committee, and the improved distribution developed here are evaluated. Only the improved equations are accurate over many system parameters.