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Showing papers on "Earthquake resistant structures published in 1999"


Journal ArticleDOI
TL;DR: In this paper, the experimental results from three half-scale unreinforced brick walls retrofitted with vertical composite strips are presented, and the specimens were subjected to cyclic out-of-plane loading.
Abstract: Unreinforced masonry (URM) buildings perform poorly under seismic forces and have been identified as the main cause of loss of life in recent earthquakes. Many of these structures fail in out-of-plane bending due to the lack of reinforcement. In this study, the experimental results from three half-scale unreinforced brick walls retrofitted with vertical composite strips are presented. The specimens were subjected to cyclic out-of-plane loading. Five reinforcement ratios and two different glass fabric composite densities were investigated. The mode of failure is controlled by tensile failure when wider and lighter composite fabrics are used and by delamination when stronger ones are used. The tested specimens were capable of supporting a lateral load up to 32 times the weight of the wall. A deflection as much as 2% of the wall height was measured. Although both URM walls and composite strips behave in a brittle manner, the combination resulted in a system capable of dissipating some energy. Retrofitting UR...

146 citations


Journal ArticleDOI
TL;DR: In this article, a hysteretic model was proposed to model the effects of connection weld fractures in beam-to-column connections in welded special moment-resisting frames during the 1994 Northridge earthquake.
Abstract: The Northridge earthquake of 1994 led to numerous weld fractures in beam-to-column connections in welded special moment-resisting frames. To address building performance issues raised by these failures and to support improvements in probability-based load resistance factor design for steel building structures, four welded special moment-resisting frames of different sizes and configurations that suffered connection damage during the earthquake are evaluated using both deterministic and stochastic approaches. The results of this investigation are presented in two companion papers. This paper focuses on deterministic dynamic modeling issues, using a new hysteretic model that incorporates the effects of connection weld fractures on building response and ground motions believed to be representative of the Northridge earthquake. The degraded connection model results in somewhat larger frame deformations, but its impact only becomes significant at spectral accelerations larger than those believed to have occurred. The agreement of predicted and surveyed damage was quite good for two of the frames, but not as good for the other two. Inherent randomness and modeling uncertainties limit the quality of the agreement that is possible from a single deterministic analysis. Thus, in the companion paper, the role of uncertainties in making such comparisons is investigated. Randomizing the strength and ground motion yields a probabilistic description of building performance that places such comparisons of predicted and observed damage in better perspective.

126 citations




01 Jan 1999
TL;DR: In this paper, the authors provide background information on earthquake generating plate tectonics in the Japanese archipelago, historical seismicity and development of fault rupture in the region during the Kobe earthquake.
Abstract: The paper provides background information on earthquake generating plate tectonics in the Japanese archipelago, historical seismicity and development of fault rupture in the region during the Kobe earthquake. The geological setting and topography are described together with the expansion of land reclamation in the port area of Kobe. Characteristics of the ground motions recorded at various sites during the earthquake are also presented. Soil conditions investigated at two sites by way of undisturbed sampling using ground freezing technique are described. Features of liquefaction and consequent lateral spreading which occurred in the reclaimed fills are presented in terms of attenuation characteristics of the lateral displacement of the ground diminishing with distance inland from the waterfront. Outcome of comprehensive investigation on the damage to foundations of LPG storage tanks is described with emphasis on the behavior of precast reinforced concrete piles. Simple analyses were made for the behavior of piles undergoing lateral spreading.

68 citations


Journal ArticleDOI
TL;DR: In this article, a model for predicting punching shear failures at interior slab-column connections was developed based on experimental results obtained at various universities and incorporated into a new RC slab element for the nonlinear analysis program, DRAIN-2DM, along with the desired unloading behavior when a punch occurs.
Abstract: A model for predicting punching shear failures at interior slab-column connections was developed based on experimental results obtained at various universities. This model has been incorporated into a new RC slab element for the nonlinear analysis program, DRAIN-2DM, along with the desired unloading behavior when a punch occurs. A four-story RC frame office building that experienced punching shear failures during the Northridge earthquake was evaluated using this new model and the occurrence of punching shear failures was successfully postcalculated for the ground motion recorded nearest the structure. The study building was evaluated for three ground motions scaled to the same peak ground acceleration. The building response varied for each record, but in general, it was found that the inclusion of punching shear failures can modify the overall building response in terms of drift, fundamental period, inelastic activity, and base shear distribution. In the case of the study building, the presence of the st...

65 citations


Journal ArticleDOI
TL;DR: In this article, the authors investigated the adequacy of a seismic retrofit strategy that relies instead on ductile end-diaphragms inserted in the steel superstructure: the objective is to protect the substructure by re-positioning the steel diaphrasms over abutments and piers with specially designed ductile diaphragm calibrated to yield before the strength of the substructures is reached.
Abstract: Steel bridges are frequently supported by seismically vulnerable substructures, as clearly dem- onstrated by recent earthquakes. The seismic retrofit of these nonductile substructures can be, in many cases, a rather costly operation. This paper investigates the adequacy of a seismic retrofit strategy that relies instead on ductile end-diaphragms inserted in the steel superstructure: the objective is to protect the substructure by re- placing the steel diaphragms over abutments and piers with specially designed ductile diaphragms calibrated to yield before the strength of the substructure is reached. For a type of steel slab-on-girder bridge widely found in North America, this paper presents simplified analytical models as well as a step-by-step design procedure developed for three types of ductile diaphragm systems (such as shear panels, eccentrically braced frames, and triangular-plate added damping and stiffness devices), followed by results from nonlinear inelastic analyses conducted to investigate the seismic behavior of these retrofitted bridges. At this time, only bridges on stiff substructure are considered, although a few examples are presented to illustrate the potential inadequacy of this retrofit approach for bridges on flexible substructures.

46 citations


Journal ArticleDOI
TL;DR: In this paper, a seismic retrofit strategy was proposed to protect the substructures of existing steel slab-on-girder bridges from damage during earthquakes. But the results from an experimental program to investigate the adequacy of some proposed details were presented.
Abstract: Ductile end diaphragms have been proposed as a seismic retrofit strategy to protect the substructures of existing steel slab-on-girder bridges from damage during earthquakes. This paper presents the results from an experimental program to investigate the adequacy of some proposed details. Cyclic tests on full-size girder specimens having the proposed ductile diaphragms demonstrate that these can possess adequate initial elastic stiffness, strength, and capacity to dissipate hysteretic energy in the intended manner. The specimens developed a rotational capacity of 0.2 rad when energy dissipation devices of the TADAS (Triangular-plate Added Damping And Stiffness) type were used, and link distortion angles of 0.08 to 0.11 rad when eccentrically braced frame and shear panel systems were in place, corresponding to average ductilities of 8 to 10 before failure. Better performance of the eccentrically braced frame system would have been possible had lateral support been provided at the ductile link. However, ductile end diaphragms having bolted connections suffered significant slippage, leading to pinched hysteretic curves. Tests show that welding significantly improves the seismic behavior of these ductile systems. Specimens with nominal channel diaphragms and those without any diaphragm dissipated significantly less hysteretic energy, and suffered bolt rupture, buckling of the web stiffeners, and fracture of the stiffeners welds at large drifts.

44 citations


Book
01 Jun 1999
TL;DR: In this paper, the authors evaluated the performance of reinforced concrete structures with respect to the impact of seismic deformation on their structural resilience to earthquakes using a probabilistic displacement spectra (PDS) method.
Abstract: Section 1: Earthquake resistant analysis and design On the evaluation of probabilistic displacement spectra Random vibration of structures with strong non-linearities subjected to seismic excitation Evaluation of proper supplemental damping for a multi-story steel frame using capacity spectrum method Seismic design - classic and new approaches Estimation method of requisite strength to control deformation of RC structure under earthquake motion and investigation of the accuracy Plastic energy as a design parameter Strength reduction factors for structures that simultaneously dissipate plastic and viscous energy Seismic response of buildings with setback Effect of structural irregularities and short columns on the seismic response of buildings during last Turkey earthquakes Stochastic seismic induced effects in dam-reservoir systems Equivalent SDOF systems for the estimation of seismic response of multistory frame structures Re-evaluation of seismic capacity of interior beam-column joints. Section 2: Seismic risk reduction Optimal strategies for seismic risk reduction Performance of distributed base isolation system for masonry buildings Importance of eccentricities in the superstructure on the torsional response of base-isolated structures Design and characteristics of high damping natural rubber bearings for base isolation Seismic isolation and site effects, an inter-disciplinary investigation at the seismic test site INCERC, Bucharest, Romania A new elastic-plastic dissipation device for seismic protection of the bridge pier structures: design and numerical investigation Ground motion and structural vibration reduction using periodic wave barrier as a passive isolation Self variable stiffness system for optimal seismic response of RC frame with concrete braces Effects of damping matrix in the response of structures with added linear viscous dampers A building with TLD to earthquake Employing glass panels with rounded corners to mitigate seismic damage in architectural glass wall systems Reducing hazards due to architectural elements in buildings subject to earthquakes Time-domain analysis of structures with dampers modelled by fractional derivatives Numerical simulation of structures equipped with friction energy dissipation devices subjected to seismic load Using genetic algorithm for optimal control force in active vibration control. Section 3: Building structures The performance of reinforced masonry piers subjected to horizontal cyclic loading Requirements for performance based design of buildings Pseudodynamic tests on full scale masonry walls Seismic-damage quantification for brick infills of RC frames. Section 4: Reinforced concrete structures A comparison of nonlinear models for reinforced concrete frames Model simulation of damage pattern and response of multi-storeyed RCC framed structure subjected to ground shock The influence of P-? effects on seismic response of RC framed structures The review of strut and tie models suggested for exterior beam column connections Seismic design of R/C frames: An assessment of the behaviour factor Failure mechanism of RC beam under reversed cyclic loading after flexural yielding caused by lateral strain accumulation in plastic-hinging region Stress-strain behavior in compression of lightweight fiber reinforced concrete under monotonic and cyclic loads Comprehensive behaviour of R.C. members strengthened with carbon fiber reinforced plastic layers Reliability of pushover analysis - based methods for seismic assessment of R/C buildings Two parameters analysis of post-peak dynamic behaviour of high performance concrete Performance based modeling and evaluation of joint mechanics. Section 5: Retrofitting and repairs Assessment of the seismic resistant capacities of traditional masonry buildings and retrofitting interventions to reduce their vulnerability Three-dimensional IT investigation of seismic distress in a large existing structure and development of remedial measures Seismic upgrade of a reinforced concrete building Retrofitting of large water retaining structures to withstand earthquakes Some experiences about the retrofitting of tower masonry structures Retrofitting of reinforced concrete beams using externally bonded FRP plates Repair of slab-column connections using CFRP Calculation of costs for seismic rehabilitation of historical buildings. Section 6: Soil dynamics Harmonic response of a rigid wall retaining poroelastic soil by direct approach Numerical analysis of non-linear soil-structure interaction Identification of dynamic soil resistance to piles with consideration of system uncertainties Development of an in situ method to measure nonlinear soil behavior Spatial distribution of the ground motion during the 1999 Chi-Chi earthquake based on the wavelet transform Comparison between numerical and experimental behaviour of granular soil. Section 7: Underground and lifeline structures Seismic design of tunnels Inelastic response of 3-D underground structures in rock under seismic loading Dynamic response of underground structures in soils with variable mechanical properties Seismic design of buried pipelines for liquefaction-induced large ground displacement Pre-stressed concrete large-diameter pipes: joint behaviour during earthquakes. Section 8: Bridges Study on the seismic retrofit of a steel cable-stayed bridge Investigation of earthquake resistance and cost effect on hybrid cable-stayed bridge with two girders Masonry bridge with five long span arches: computer modelling analysis of failures and repairs Vulnerability of Pony Truss bridges Study of the nonlinear behavior of the prestressed concrete girders by a neural network Seismic analysis and design of R/C bridge including SSI effects Static and dynamic behaviour of an historical stone bridge investigated by means of a 3D numerical model. Section 9: Special Structures A 3-D boundary element model for the dynamic analysis of arch dams with porous sediments Seismic response of Mullardoch Dam: a case study Seismic response of thin shell storage tanks Seismic response of a historical Mamluk style minaret Low cost earthquake resistant reinforcement for adobe houses.

34 citations


Journal ArticleDOI
TL;DR: In this paper, the authors investigated the seismic behavior of reinforced concrete beam-column T-joints in multicolumn bridge frames constructed in California in the 1950s and 1960s.
Abstract: Experimental tests and analyses investigated the seismic behavior of reinforced concrete beam-column T-joints. The test specimens were representative of interior beam-column joints in multicolumn bridge frames constructed in California in the 1950s and 1960s. Three one-third scale models were tested, one representing the as-built joint and two representing retrofit joints. The as-built specimen had relatively little ductility capacity, whereas the retrofitted specimens exhibited improved performance. The nominal joint stress state, joint force-transfer mechanisms, and bond stress characteristics were investigated as a means of assessing joint behavior. This study clarifies the seismic behavior of lightly reinforced bridge T-joints and verifies a design procedure for retrofitting these joints.

31 citations


Journal ArticleDOI
TL;DR: In this article, the authors analyzed the non-linear seismic response of reinforced concrete slit shear walls under earthquake excitation and showed that yielding of the connecting beams can significantly reduce the deflection response of the slit-shear wall structure and the seismic loading induced on it.

Journal ArticleDOI
TL;DR: In this article, the authors investigated the feasibility and advantages of applying the retrofit measures developed for single-column bent bridges to multiconnection bent bridges and proposed the most effective measures for strengthening bridges.
Abstract: Many retrofit measures have been proposed and then implemented into existing highway bridges. The goal of seismic strengthening is not intended to retrofit a bridge to be "earthquake-proof", but to minimize the likelihood of structural collapse. An amount of acceptable damage may occur during a design level earthquake. The combination of retrofit measures and the acceptable damage greatly complicates the structural properties for a bridge. It is necessary to use analytical and experimental means to verify the effectiveness of various retrofit combinations. The objectives of this research are: (1) to investigate analytically the feasibility and advantages of applying the retrofit measures developed for single-column bent bridges to multi-column bent bridges; (2) to evaluate analytically the effects and benefits of current column retrofit strategies for multi-column bridges and propose the most effective measures for strengthening bridges; (3) to evaluate the performance of earthquake restrainers and find the change of seismic loads and displacements caused by their installation. To achieve the objectives, an existing nonlinear dynamic bridge analysis program with elastic-perfectly plastic column behavior and a conventional hysteresis model was modified in order to include softening behavior and a more realistic hysteresis rule for cyclic loading. Both two- and three-dimensional structural models for two actual bridges from Washington were analyzed by inputting a typical seismic record. The two-dimensional models were used to evaluate column retrofitting measures, and the three-dimensional model was used to evaluate the performance of longitudinal earthquake restrainers. Both partial and full column retrofit strategies were shown to result in decreased maximum earthquake response and decreased plastic deformation of columns for the bridge bent compared to the case without retrofitting. Therefore, it was concluded that the partial column retrofit strategies were feasible after a ductility capacity of the bridge is exactly defined. The opening displacements at expansion joint hinges were decreased due to the installation of longitudinal restrainers. Additionally, the redistribution of earthquake forces caused by their installation was not significant.

01 Jan 1999
TL;DR: In this article, the Friction Pendulum bearings were used to achieve an elastic, no-damage seismic design, and provided the lowest total construction cost for this performance level for bridges.
Abstract: This paper presents recent examples of bridges seismically isolated using Friction Pendulum seismic isolation bearings The Friction Pendulum bearings were used to achieve an elastic, no-damage seismic design, and provided the lowest total construction cost for this performance level

01 Jan 1999
TL;DR: In this paper, the authors have shown that the limiting drift capacity of a reinforced concrete column proportioned to resist earthquake effects through energy dissipation in the nonlinear range of response may be determined simply by considering two parameters: 1) the aspect ratio, and 2) the transverse reinforcement index.
Abstract: The current seismic design philosophy allows nonlinear behavior of the structure to reduce strength requirements. This implies that the structure must be able to retain its integrity under cycles of displacement into the nonlinear range. The structure has to be tough. Evaluation of experimental results from 15 series of tests reported by various investigators has shown that the limiting drift capacity of a reinforced concrete column proportioned to resist earthquake effects through energy dissipation in the nonlinear range of response may be determined simply by considering two parameters: 1) the aspect ratio, and 2) the transverse reinforcement index.

Journal ArticleDOI
TL;DR: In this paper, the authors presented a new retrofit technique to restore the capacity of the columns and to improve ductility of bridge columns by replacing dowel bars in the footings and lap splices at the base of columns.
Abstract: A large number of bridges in the United States have been identified as having potentially inadequate detailing to resist earthquakes. A common deficiency in many columns of these bridges is short dowel bars in the footings and short lap splices at the base of the columns. In addition, the columns are poorly confined and lack adequate shear strength. This paper addresses these deficiencies in oblong tapered bridge columns and presents a new retrofit technique to restore the capacity of the columns and to improve ductility. Six 0.4 scale model specimens were constructed and tested. The first two specimens represented as-built details of existing bridge columns: one with a fixed-base detail and the other with a one-way hinge detail. The other four specimens were identical to the two as-built models, but were retrofitted to address their deficiencies. Unlike steel jackets used in previous studies, the jackets used in this study were connected to a base plate that was anchored to the footing. This detail was necessary because of the short anchorage of starter bars in the footings. Results from testing the four retrofitted specimens showed that the adopted retrofit technique enabled the columns to reach their design strength under cyclic lateral loading. The retrofit also enhanced the shear strength and the ductility of the columns.

Journal Article
TL;DR: In this paper, a full-scale, dynamic testing and evaluation program of readily available seismic isolation and energy dissipation systems is presented to increase the confidence level of bridge owners and lead them to consider and use isolation/damping technology cost-effectively to protect otherwise vulnerable structures from more severe earthquake damage.
Abstract: During the past 2 decades, bridge engineers have gained a better understanding of the behavior of structures during an earthquake The ductility-design philosophy is the mainframe of modern seismic-design guidelines in the United States and most countries abroad While this design philosophy provides safety against collapse, it tends to be costly because of the damage induced in plastic-hinge zones and to the severe lateral displacements that can occur even in a moderate earthquake Therefore, in recent years, design engineers have sought an alternative design philosophy that avoids or limits damage to a bridge to maintain postearthquake serviceability Seismic isolation has emerged as one of the most promising retrofitting strategies for improving the seismic performance of existing bridges It is also an attractive approach for new construction when conventional design is not suitable or economical In January 1994, the Federal Highway Administration, California Department of Transportation, and the Highway Innovative Technology Evaluation Center cooperated in launching a full-scale, dynamic testing and evaluation program of readily available seismic isolation and energy dissipation systems A total of 11 domestic and international manufacturers completed the testing program The program is expected to increase the confidence level of bridge owners and lead them to consider and use isolation/damping technology cost-effectively to protect otherwise vulnerable structures from more severe earthquake damage In addition, it will provide useful data to academic researchers

01 Jan 1999
TL;DR: In this paper, the Polar Street Bridge over the Mississippi River at St. Louis was evaluated and a seismic retrofit strategy was developed for the 660 meter (2,165 foot) structure consisting of two parallel five span continuous roadways with orthotropic steel plate deck and variable depth steel box girders.
Abstract: In work for the Missouri Department of Transportation (MoDOT) Sverdrup Civil, Inc. performed a seismic evaluation and developed a seismic retrofit strategy for the Polar Street Bridge over the Mississippi River at St. Louis. The 660 meter (2,165 foot) structure consists of two parallel five span continuous roadways with orthotropic steel plate deck and variable depth steel box girders. The seismic evaluation considered three levels of design earthquakes and identified deficiencies in the bearings, reinforcement splices in the columns and piers, and one foundation. The retrofit strategy includes adding force transmitters or dampers to the existing expansion bearing piers, adding transverse shear blocks to the beam seats, jacketing the column splices, adding rock anchors to one foundation, and adding supplemental reinforcement to address lap splice deficiencies at the base of the piers.

01 Jan 1999
TL;DR: In this paper, the authors present the aspects of design and detailing with headed reinforcement for seismic resistance and concrete material performance as it is modified by headed reinforcement, including empirical equations, strut-tie modeling procedures, a new membrane stress theory, and a cyclic reinforcing bar bond-slip theory.
Abstract: Headed reinforcement uses one or more anchorages, called heads, attached to the end(s) of steel reinforcing bars. Such heads serve to develop a bar in a relatively short distance, and can also better confine the interior concrete. For over a decade, headed reinforcement has had extensive field use in major structures subjected to cyclic fatigue and dynamic loading, as well as thorough laboratory testing on both bare steel bars as well as on concrete members with headed reinforcement. Such tests have also demonstrated the superior performance of headed reinforcement under seismic loading conditions, even in high moment zones, and joint regions. Presented here are the aspects of design and detailing with headed reinforcement for seismic resistance, and the aspects of concrete material performance as it is modified by headed reinforcement. Specific advanced design tools are discussed including empirical equations, strut-tie modeling procedures, a new membrane stress theory, and a new cyclic reinforcing bar bond-slip theory, together with design examples for bridge structures. Currently, ACI 349, CSA 474, and several overseas codes provide design rules for headed reinforcement. Where necessary these rules may be supplemented by experience, engineering judgement, empirical guidelines, and test results. New standards, regarding the use of headed reinforcement in concrete are pending with both ASTM and ACI 318; which when incorporated should further facilitate the design process.

01 Jan 1999
TL;DR: In this paper, some new conforming procedures to improve the ductility of MR frames were examined by means of local and global analyses, and the results indicate the superiority of modified moment resisting frames, designed according to the "dogbone" and "reinforced" concepts, as compared with the other configurations, considering the ductile requirements by different sever ground motions.
Abstract: In this paper some new conforming procedures to improve the ductility of MR frames were examined by means of local and global analyses. The results indicate the superiority of modified moment resisting frames, designed according to the ‘dogbone’ and ‘reinforced’ concepts, as compared with the other configurations, considering the ductility requirements by different sever ground motions. 1. INTRODUCTION The design philosophy of modern codes for earthquake resistant structures is based on the ability to dissipate energy through plastic deformations. It is generally recognized that, in order to design ductile moment resisting frames, dissipative zones have to be located in the beams ends rather than in the columns, leading to a collapse mechanism of the global type (Mazzolani & Piluso, 1996). So, the primary aim of the aseismic design is to achieve the balance between strength and ductility, avoiding collapse mechanisms having unsatisfactory energy dissipation capacity (i.e. storey mechanisms), by a proper proportioning and detailing of the structural elements. During the recent earthquakes, Northridge (1994), Kobe (1995), many brittle fractures of welded moment resisting frames, mainly located at the beam-column connections, were found, as well as unpredicted ‘storey mechanisms’ in the mid stories of the steel structures were observed. These recent events demonstrated that for an efficient earthquake design in highly seismic areas two aspects must be considered: firstly, the failure mode and ductility control must be assured, secondly, the important differences between the influencing earthquake characteristics (near-source vs far-source) must be

01 Jan 1999
TL;DR: In this paper, a performance-based design procedure for confinement steel, developed based on the experimental findings, is presented, where the suggested design procedure is compared with relevant provisions of some design codes, and a performance analysis of column-stub specimens with concrete strengths ranging between 72 MPa and 102 MPa were tested under constant axial load and reversed cyclic displacement excursions.
Abstract: This paper presents results from an extensive research program which aims to study confinement of concrete by lateral reinforcement. The current work deals with the comparison of seismic performance of ultra high strength concrete (UHSC) columns with high strength concrete (HSC) and normal strength concrete (NSC) columns. In the experimental part of the current study, column-stub specimens with concrete strengths ranging between 72 MPa and 102 MPa were tested under constant axial load and reversed cyclic displacement excursions. A performance based design procedure for confinement steel, developed based on the experimental findings, is presented here. The suggested design procedure is compared with relevant provisions of some design codes.