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 Fragility Assessment of Lightly Reinforced Concrete Structural Walls

Development of fragility functions is a pertinent stage in seismic performance assessment of structures. A database of lightly Reinforced Concrete (RC) walls under simulated seismic loading is compiled from the literature to establish the drift-based seismic fragility functions. To classify the damage states experienced by RC walls, the Park-Ang Damage model is amended in this research. Then, the modified Bouc-Wen-Baber-Noori hysteresis model is implemented in ABAQUS to predict the hysteresis behavior of RC walls. Thereafter, the proposed hysteresis model is employed to develop the seismic fragility curves of low to mid-rise RC walls in Singapore using incremental dynamic analysis approach.     

Performance-Based Vulnerability Assessment of Multi-Story Reinforced Concrete Structures Exposed to Pre- and Post-Earthquake Fire

Post-earthquake fire can potentially bring about much more damage than the earthquake itself. Performing a vulnerability assessment for a structure that has already sustained damage in an earthquake and is then exposed to fire is therefore of importance. This paper describes a performance-based investigation in which applied loads to a structure are appropriately quantified. To do so, a sequential structural analysis is performed on the Life Safety performance level of a three-story reinforced concrete frame selected from a building. For the analysis to be more realistic, the slab is also included in the frame analysis through the concept of effective length. The frame is first subjected to an earthquake load with the PGA of 0.30 g followed by a fire analysis, using the ISO834 fire curve and the iBMB fire curve. The time needed for the structure weakened by the earthquake to collapse under fire is then calculated. As a benchmark, fire-only analysis is also performed for the undamaged frame. Moreover, the effect of thermal spalling is considered in the slabs. The selected frame is evaluated under various failure criteria such as load capacity, displacement, and rate of displacement. The results show that no failure is observed when the frame is exposed to fire alone, either when using the ISO curve or the iBMB curve under various failure criteria. It is also shown that while the PEF resistance based on load capacity criteria under the ISO curve is around 120 minutes, it reduces to about 95 min under the iBMB curve. However, considering the rate of deflection failure criteria, the PEF resistance is around 103 min and 75 min under the ISO and the iBMB curves, respectively. It is then concluded that in the PEF analysis, the iBMB curve is more compatible with the concept of performance-based design than the ISO curve is.     

Seismic Fragility Evaluation of Lightly Reinforced Concrete Beam-Column Joints

Fragility functions play an essential role in evaluating the seismic vulnerability of structures. To establish the seismic fragility functions of lightly Reinforced Concrete (RC) beam-column joints, the Park-Ang Damage model has been amended to quantify the damage states and the modified Bouc-Wen-Baber-Noori model has been employed and implemented in ABAQUS to predict the structural hysteresis behavior. Following successful calibration of the numerical results of a RC test frame from literature, the proposed model has been utilized to assess the seismic fragility curves of low to mid-rise RC frames in Singapore for 30 scaled ground motions using incremental dynamic analysis approach.     

Experimental Study on Self-Centering Concrete Wall with Distributed Friction Devices

A self-centering concrete wall with distributed friction devices is proposed to achieve seismic resilient building structures. Unbonded post-tensioned tendons, running vertically through wall panels, provide a restoring force that pulls the structure back toward its undeformed plumb position after earthquake. Two steel jackets are installed at wall toes to prevent concrete spalling and crushing. Friction devices are distributed between the wall and its adjacent gravity columns to achieve controllable energy dissipation, and these devices are readily replaceable. Desirable self-centering and energy dissipation capacities were observed in low-cyclic loading tests, and influences of various parameters on the hysteretic behavior were investigated.     

Fiber-Based Modeling of Circular Reinforced Concrete Bridge Columns

This article presents the application of fiber-based analysis to predict the nonlinear response of reinforced concrete bridge columns. Specifically considered are predictions of overall force-deformation hysteretic response and strain gradients in plastic hinge regions. This article discusses the relative merits of force-based and displacement-based fiber elements, and proposes a technique for prediction of nonlinear strain distribution based on the modified compression field theory. The models are compared with static and dynamic test data and recommendations are made for fiber-based modeling of RC bridge columns.     

Characterization of Ductility and Inelastic Displacement Demand in Base-Isolated Structures Considering Cyclic Degradation

New designed or retrofitted structures with the use of isolation system may exhibit nonlinear deformations during strong ground motions. Inelastic displacement ratio of base-isolated structures is studied in this paper by employing two degree of freedom model taking into account inelastic behavior of isolators and superstructure. Parametric study is conducted to evaluate influence of isolator and superstructure properties on inelastic displacement ratio according to two sets of near-fault and far-fault ground motions. Accuracy of proposed equations in the literature to evaluate inelastic displacement ratio are studied, as well. Furthermore, cyclic degradation effects are investigated by considering stiffness and strength degradation and pinching in hysteresis model of superstructure. Eventually, inelastic responses of isolated structures with two types of isolators (lead rubber bearing and friction pendulum bearing) are compared.     

Investigation of the Seismic Behavior of a Historical Masonry Minaret Considering the Interaction with Surrounding Structures

This study examines the seismic behavior of the minaret of the well-known historical structure “Sultan Ahmed Mosque” under strong earthquake motion. Despite their slenderness and height, minarets are towers with well-established earthquake resistance. In general, these structures were constructed adjacent to the main structure and/or its components. Hence, it is expected that the dynamic behavior of the minarets is influenced by the dynamic characteristics of the adjacent structures as well as the contact conditions. In the presented study, the dynamic behavior of the M6 minaret of the Sultan Ahmed Mosque, which is in contact with the portico that surrounds the courtyard of the mosque, is considered. Ambient vibration tests were conducted on site in order to identify the individual and coupled vibration modes of the minaret and the portico. A finite/discrete model was developed and seismic analysis was carried out. The comparative study reveals considerable differences in responses of different models under strong and very strong earthquake motion.     

Material Modeling in the Dynamic Nonlinear Analysis for Recycled Aggregate Concrete Structures

Dynamic mechanical tests of recycled aggregate concrete (RAC) test units confined by transverse hoop reinforcement are carried out. The effects of the strain rate, hoop reinforcement confinement, and replacement ratio of recycled coarse aggregate (RCA) on the mechanical properties of confined recycled aggregate concrete (CRAC) are thoroughly analyzed and assessed. The strain-rate-dependent constitutive model of CRAC is proposed for the high strain rate representative of seismic conditions. A three-dimensional discrete numerical model, based on the proposed rate-dependent material model of CRAC, is established to investigate and evaluate the dynamic nonlinear behaviors of RAC structures.     

Mapping Mesolithic and Neolithic cultures behaviours and interactions with nature and properties of rocks in Western France

Multivariate statistical methods are used to study recent Prehistory lithics from the Armorican Massif, allowing us to classify them in more or less distinct groups according to the structural and mineralogical qualities of rock types involved. Analyses are carried out on metamorphic, sedimentary and magmatic rocks making up lithics collected from 31 localities. The petrographic properties are determined by polarizing microscope (POM), while the mechanical properties are obtained by Vickers's indentation method (VI), compression/traction (CT) and ultrasound echography (UE). The results provide us with important information about the management of lithic raw materials used by various human and cultural groups during the Mesolithic and Neolithic of the Armorican Massif. The more commonly used materials show a homogeneous and stable distribution of regional technology styles. The rock types exhibiting mature and homogeneous structures possess the better qualities for knapping (fracture energy G_Ic) and use (edge toughness M₁), and are more involved in exchange. The application of Upward Hierarchical Classification (UHC) and Principal Component Analysis (PCA) allows us to identify the classes of materials as well as the causes of variations of rock type abundance within the lithic assemblages of the Mesolithic and the Neolithic. In this way, we can then also predict the discovery of archaeological artefacts in areas lacking any known indications of the exploitation of outcropping materials.