Section 5 : Damage to the transportation infrastructure

This section describes damage sustained by the transportation infraestructure as a result of the Marmara earthquake in Turkey on August 17, 1999

Design and retrofit methodology for building structures witn supplemental energy dissipating systems

The study described in this report on focuses on fundamental issues related to the design and use of supplemental damping devices in building structures. The principle objective is to develop a generic/practical analysis and design methodoly for structures that considers structural velocities and equivalent viscous damping of the devices. These two issues are explored in depth. Tools to transform the spectral velocity to an actual relative structural velocity are provided, and simple design procedure which incorporates power equivalent linear damping based on actual structural velocities is presented. The effectiveness of the design methodology is demonstrated with a retrofit design example using a supplemental load balancing tendom configuration

Truss modeling of reinforced concrete shear-flexure behavior

A reinforced concrete beam-column, assumed to possess a series of potential crack planes, is considered as a truss consisting of a finite number of differential truss elements and analyzed using the virtual work method to define the lateral force-deformation relationship. The differential truss is simplified using various numerical integration schemes, since the analytical integration involves the complexity. From such truss models the effects of the diagonal shear cracking can be reliably modeled and valuable information such as crack angles and the cracked elastic stiffness in both shear and flexure can be determined. An equation to estimate the theoretical crack angle is derived by considering the energy minimization on the virtual work done by shear and flexural components. Theoretical crack angles compare favorably with experimentally observed crack angles reported by previous researchers. It is postulated that the total shear strength can be found by combining three complementary mechanims that arise from: truss action that incorporates the transverse hoop steel; truss action that incorporates the concrete tensile strength normal to the principal diagonal crack plane; and arch action that incorporates the axial load transferring mechanism. Displacement compatibility requirements are applied when combining the three mechanism to give the overall shear force-deformation behavior. The theory is also implemented computationally using cyclic non-linear truss elements. However, the present version of modeling technique cannot properly account for the cyclic loading effect due to the earthquake duration effect. If improved constitutive models were used to more faithfully represent concrete and steel behavior (under cyclic loading), then the overall predictions should also markedly improve

Experimental study on the seismic design and retrofit of bridge columns including axial load effects

This research is concerned with validation of alternative theories for seismic design and retrofit of bridge structures. The intent of these methodologies is to not only maintain life safety of bridges in a strong eartquake, but also to control damage while accommodating large seismically-induced deformations in order to maintain post-earthquake serviceability. The primary purpose of this research endeavor is to verify that both Control and Repairability of Damage (CARD) and Retrofit, Control and Repairability of Damage (ReCARD) sacrificial fuse-bar plastic hinge details have adequate fatigue life under realistic seismic loading -including the effects of variable axial loads that arise from a combination of the framing action of multiple column pier bents and vertical ground motion. As a secondary purpose, a new technique called Quasi-Earthquake Displacement (QED) Experimentation is developed to verify the CARD and RECARD construction details. The experimentation is developed to verify the CARD and ReCARD construction details. The experimental technique uses a non-linear time-history computational simulation to predict seismic displacements (and forces) in a prototype structure. These earthquake-induced actions are scaled to permit laboratory experiments to be conducted on reduced scale subassemblages of the prototype structure. It is concluded that reinforced concrete bridge columns that possess sacrificial/replaceable fuse-bars have sufficient cyclic capacity under the most adverse seismic loading conditions (including large axial load variation) to sustain a strong foreshock, mainshock and aftershock

Fatigue analysis of unconfined concrete columns

Current seismic design codes which ain at maximizing the overall ductility of a structural system are a result of extensive experimental and analytical research over the past three decades. In seismic bridge engineering, the state-of-the-practice has lagged by some two decades the state-of-the-knowledge. Thus the vast majority of the bridge structures in most countries, including the United Sates, have been built to non-seismic codes.(AU)

Capacity design and fatigue analysis of confined concrete columns

The capacity design philosophy requires the identification of all potential failure mechanisms. A preferred failure mechanism is chosen and efforts are made, through design detailing, to suppress all other undesirable failure modes. For the seismic design of bridges, the preferred failure mechanism is ductile flexural hinging of the reinforced concrete columns in the substructure. The undesirable failure modes that must be suppressed by design are three: concrete failure due to lack of confiment. buckling of the longitudinal reinforcement, and shear failures both within and outside the plastic hinge zone.(AU)

Capacity design of bridge piers and the analysis of overstrength

The capacity design philosophy has now become the design norm for the seismic design of most structural systems. For bridge systems, this means it is necessary to assess the overstrength capacity of columns prior to proceeding with the design of the foundation and superstructure. This reseach is devoted to developing deterministic procedures to obtain overstrength factors for column elements. For this purpose a moment-curvature appoach is explored. A parametric study is then conducted to investigate the factors that effect overstrength. A simplified design methodology is proposed based on plastic analysis of overstrength moment capacity. A design example shorwing the step by step procedure is also presented (AU)

Seismic design of bridge columns based on control and repairability of damage

This report describes the development of a new seismic desing paradigm referred to as Control and Repairability of Damage (CARD). replaceable/renewable sacrificial plastic hinge zones that use fuse-bar details form the basis of the approach. hinge zones are deliberately weakened with respect to their adjoining elements; all regions outside the hinge zones are detailed to be stronger than the sacrificial hinge (fuse) zone and remain elastic during seismic loading. To validate the proposed new desing philosophy, an experimental investigation was conducted. Three-one-third scale model columns (279 mm diameter and 1524 mm high) and one near full-size scale model column (610 mm diameter and 3048 mm high) were constructed and tested under a variety of cyclic loading regimes. The experiments verified that this new approach to construction enables rapid restoration to full service inmediately following an earthquake. The low cycle fatigue theory is shown to predict well the plastic rotation-life of bridge columns- no special calibration of the theory was needed for this purpose. Moreover, force-displacement hysteretic behavior and fatigue life of columns with fuse-bar detailing can be accurately predicted computationally using fiber element analysis. (AU)

Seismic resistance of bridge piers based on damage avoidance design

Current seismic resistant design practice is based on economic (limited strength) and life safety (large displacement capacity) considerrations. The seismic design philosophy that seeks to achieve these objectives is based on ductile detailing of plastic hinge regions. For a given pushover curve and effective viscous damping, the expected seismic displacement may be predicted by comparing it to the elastic desing spectra (demand). To valide the proposed design philosophy, the seismic performance of a near full-size precast concrete rocking column sbstructure was investigated. Under large lateral (rocking) displacements, no damage to either the concrete column connection or foundation was observed. The strength and stiffness was observed to remain the same after mannny cycles of loading. A complete force-deformation model for the rocking column accounting for: structural flexibility (pre-rocking), rigid body kinematics (pos-rocking) and the prestressing action of the tendons is proposed. Good agreement between the predictive theory and the experimentally observed force-deformation results was demonstrated.

How can energy based seismic design be accommodated in seismic mapping

In conventional seismic design, design loads and/or displacement are obtained from elastic spectra. Such spectra are sometimes modified to account for inelastic effects. In any case the design spectra assume a pseudo-static monotonic response, even thougth it is realized that reality earthquakes are a cyclic loading phenomena. This paper addresses the cyclic loaading response of structures by posing several questions: What is the cyclic capacity of well designed ductile structures? What is the cyclic capacity of older existing non-ductile structures? How can on assess the cyclic loading seismic demands on structure? How should seismic mapping address energy based seismic design?. (AU)

Seismic performance of a model reinforced concrete bridge pier before and after retrofit

A series of experimental and analytical studies was performed on a 1/3 scale model pier before and after retrofit. The scale model represented a typical eastern U.S. non-seismically designed concrete bridge pier. The pre-retrofitted model pier was tested under quasi-static inelastic loading and was governed by flexure at moderate drift levels, but ultimately limited by the cap beam-column joint shear capacity and a subsequent loss of bond strength in improperly anchored comumn longitudinal reinforcement (AU)

Seismic evaluation of a 30 - year old non - ductile highway bridge pier before and its retrofit

An experimental investigation of the seismic behavior of a full-scale prototype cap beam-to-column subassemblage and its retrofit are reported. The pre-retrofitted prototype specimen was retrieved from a three column bent-type pier typical of bridges constructed in the eastern United States during the 1960's. The joint core of the pre-retrofitted specimen under reverse cyclic loading was attributed to anchorage loss of column steel and fatigue failure of the concrete. Retrofitting consisted of strengthening the joint core beam by providing a high strenght concrete jacket and longitudinal prestress. The retrofit aimed at aimed at providing an elastic joint and cap beam as well as enhanced column rebar anchorage (AU)

Energy based seismic design and evaluation procedures for reinforced concrete bridge columns

This project is concerned with the experimental determination and computational micromodeling of energy absorption or cyclic fatigue capacity of reinforced concrete bridge piers. The results are used with a new smooth hysteretic rule to generate seismic energy demand spectra. By comparing the ratio of energy capacity to demand, inferences of column damageability can be made.(AU)

Field testing of bridges before and after retrofitting with seismic isolation bearings

This paper reports on full-scale large-amplitude field experimental studies being conducted in conjunction with bearing component tests, results to date and their comparison with theoretical modeling predictions, for a pair of 3-span continuous slab-on-girder bridges whose existing steel bearings are being retrofitted with laminated elastomeric bearings and lead-rubber bearings. The results of this study will assist a bridge engineer to make more informed decisions among the fundamental options for analytical modeling and for seismic retrofitting of such bridges.(AU)