Murat Dicleli

Maximum length of integral bridges supported on steel H-piles driven in sand

Abstract This paper presents design recommendations for the maximum length of integral bridges built on sand. The maximum length limits for integral bridges is determined as a function of the ability of steel H-piles supporting the abutments to sustain thermal-induced cyclic lateral displacements and the flexural capacity of the abutment. First, steel H-pile sections that are capable of sustaining large inelastic deformations under monotonic loading are determined. Then, a low-cycle fatigue damage model is employed to determine the maximum cyclic deformations that such piles can sustain. Next, the nonlinear behavior of the piles and soil–bridge interaction effects are implemented in nonlinear structural models of two typical integral bridges. Static pushover analyses of these bridges are conducted to study the effect of various geometric, structural and geotechnical parameters on the performance of integral bridges subjected to uniform temperature variations. Using the pushover analyses results, design guidelines are developed to enhance and determine the maximum length of integral bridges. It is recommended that the maximum lengths of concrete integral bridges be limited to 190 m in cold climates and 240 m in moderate climates and that of steel integral bridges are limited to 100 m in cold climates and 160 m in moderate climates.

Seismic retrofitting of highway bridges in Illinois using friction pendulum seismic isolation bearings and modeling procedures

Abstract In this paper, the economical and structural efficiency of friction pendulum bearings (FPB) for retrofitting typical seismically vulnerable bridges in the State of Illinois is studied. For this purpose, a bridge was carefully selected by the Illinois Department of Transportation (IDOT) to represent typical seismically vulnerable bridges commonly used in the State of Illinois. A comprehensive structural model of the bridge was first constructed for seismic analysis. An iterative multi-mode response spectrum (MMRS) analysis of the bridge was then conducted to account for the nonlinear behavior of the bridge components and soil–bridge interaction. The calculated seismic demands were compared with the estimated capacities of the bridge components to determine those that need to be retrofitted. It was found that the bearings, wingwalls and pier foundations of the considered typical bridge need to be retrofitted. A conventional retrofitting strategy was developed for the bridge and the cost of retrofit was estimated. Next, the bridge was further studied to develop appropriate techniques for upgrading its seismic capacity using FPB to eliminate the need for seismic retrofitting of its vulnerable substructure components. It was observed that the use of FPB mitigated the seismic forces and eliminated the need for retrofitting of the substructure components of the bridge. An average retrofitting cost using FPB was calculated and found to be less than the cost of conventional retrofitting considered in this study. Thus, FPB may successfully be used for economical seismic retrofitting of typical bridges in the State of Illinois or in regions of low to moderate risk of seismic activity.

Live Load Distribution Formulas for Single-Span Prestressed Concrete Integral Abutment Bridge Girders

In this study, live load distribution formulas for the girders of single-span integral abutment bridges (IABs) are developed. For this purpose, two and three dimensional finite-element models (FEMs) of several IABs are built and analyzed. In the analyses, the effects of various superstructure properties such as span length, number of design lanes, prestressed concrete girder size, and spacing as well as slab thickness are considered. The results from the analyses of two and three dimensional FEMs are then used to calculate the live load distribution factors (LLDFs) for the girders of IABs as a function of the above mentioned parameters. The LLDFs for the girders are also calculated using the AASHTO formulas developed for simply supported bridges (SSBs). The comparison of the analyses results revealed that LLDFs for girder moments and exterior girder shear of IABs are generally smaller than those calculated for SSBs using AASHTO formulas especially for short spans. However, AASHTO LLDFs for interior girder shear are found to be in good agreement with those obtained for IABs. Consequently, direct live load distribution formulas and correction factors to the current AASHTO live load distribution equations are developed to estimate the girder live load moments and exterior girder live load shear for IABs with prestressed concrete girders. It is observed that the developed formulas yield a reasonably good estimate of live load effects in prestressed concrete IAB girders.

Performance of Seismic-Isolated Bridges in Relation to Near-Fault Ground- Motion and Isolator Characteristics

This paper investigates the performance of seismic-isolated bridges (SIBs) subjected to near-fault (NF) earthquakes with forward rupture directivity effect (FRDE) in relation to the isolator, substructure, and NF earthquake properties, and examines some critical design clauses in AASHTOs Guide Specifications for Seismic Isolation Design. It is found that the SIB response is a function of the number of velocity pulses, magnitude of the NF ground motion, and distance from the fault. Particularly, a reasonable estimation of the expected magnitude of the NF ground motion according to the characteristics of the bridge site is crucial for a correct design of the SIB. It is also found that the characteristic strength and post-elastic stiffness of the isolator may be chosen based on the characteristics of the NF earthquake. Furthermore, some of the AASHTO clauses are found to be not applicable to SIBs subjected to NF ground motions with FRDE.

SEISMIC RETROFITTING OF CHEVRON-BRACED STEEL FRAMES BASED ON PREVENTING BUCKLING INSTABILITY OF BRACES

In this research, a seismic retrofitting method for chevron-braced frames (CBFs) is proposed. The key idea here is to prevent the buckling of the chevron braces via a conventional construction technique that involves a hysteretic energy-dissipating element installed between the braces and the connected beam. The energy-dissipating element is designed to yield prior to buckling of the braces, thereby preventing the lateral stiffness and strength degradation of the CBF caused by buckling, while effectively dissipating the earthquake input energy. Nonlinear static pushover, time history and damage analyses of the CBF and retrofitted CBF (RCBF) are conducted to assess the performance of the RCBF compared with that of the CBF. The results of the analyses reveal that the proposed retrofitting method can efficiently alleviate the detrimental effects of earthquakes on the CBF. The RCBF has a more stable lateral force–deformation behavior with enhanced energy dissipation capability than the CBF. For small-to-moderate intensity ground motions, the maximum interstory drift of the RCBF is close to that of the CBF. But, for high intensity ground motions, it is considerably smaller than that of the CBF. Compared with the CBF under medium-to-large intensity ground motions, the RCBF experiences significantly less damage due to prevention of buckling of the braces.

Improved Effective Damping Equation for Equivalent Linear Analysis of Seismic-Isolated Bridges

In this study, an improved effective damping (ED) equation is proposed to obtain more reasonable estimates of the actual nonlinear response of seismic-isolated bridges (SIB) using equivalent linear (EL) analysis procedure. For this purpose, first the EL analysis results using AASHTOs ED equation is evaluated using harmonic and seismic ground motions. The effect of several parameters such as substructure stiffness, isolator properties, and the intensity and frequency characteristics of the ground motion are considered in the evaluation. Next, the effect of the superstructure mass on the ED ratio is studied. It is found that the accuracy of the EL analysis results is affected by the frequency characteristics and intensity of the ground motion. It is also demonstrated that AASHTOs ED equation should incorporate the effective period of the SIB and isolator properties for a more accurate estimation of the seismic response quantities. A new ED equation that includes such parameters is formulated and found to improve the accuracy of the EL analysis.

Critical Truck Loading Pattern to Maximize Live Load Effects in Skewed Integral Bridges

Abstract An integral bridge (IB) is one in which the abutments are cast monolithically with the deck to form a rigid frame structure. When the geometry and conditions do not allow for designing straight IBs, skewed IBs (SIBs) are designed. Current bridge design specifications are mainly developed for regular jointed bridges. Thus, provisions for SIBs have not been included in these specifications yet. Consequently, to determine live load effects in SIB components, many practicing engineers built a three-dimensional (3D) finite element model (FEM). In this study, various multiple design truck loading patterns are investigated to determine the most critical loading pattern producing the maximum live load effects in SIB components. The results of the analyses reveal that in the case of SIBs, different truck loading patterns arise when compared to bridges with no skew. Trucks that are placed diagonally across the width of the bridge are observed to produce the most unfavorable live load effects in bridge components.

Comparative Study on the Effect of Number of Girders on Live Load Distribution in Integral Abutment and Simply Supported Bridge Girders

In this study, the effect of the number of prestressed concrete girders on the distribution of live load effects among the girders of integral abutment bridges (IABs) and simply supported bridges (SSBs) is investigated. For this purpose, two and three dimensional finite element models (FEMs) of several single-span IABs and SSBs are built and analyzed. In the analyses, bridges with various superstructure properties, such as span length, girder type and size, slab thickness are considered. The finite element analyses (FEA) results are then used to calculate the live load distribution factors (LLDFs) for the girders of IABs and SSBs as a function of the number of girders. Comparison of the analyses results revealed that, LLDFs for SSBs vary slightly as the number of girders changes. However, in the case of IABs, it is found that while the LLDFs for the girder moments decrease significantly as the number of girders increases, the number of girders has a negligible effect on the LLDFs for the girder shear. Accordingly, the number of girders is added as a new parameter to the previously developed correction factors for AASHTO LRFD LLDFs for the girder moment. It is observed that the developed formulae yield a reasonably good estimate of live load effects in prestressed concrete IAB girders.

Investigation of the Applicability of AASHTO LRFD Live Load Distribution Equations for Integral Bridge Substructures

In this study, applicability of the AASHTO LRFD girder live load distribution equations (LLDEs) for integral bridge (IB) abutments and piles is investigated. For this purpose, numerous 3-D and corresponding 2-D structural models of typical IBs are built and analyzed under AASHTO LRFD live load. In the analyses, the effect of various superstructure properties such as span length, slab thickness, girder spacing and stiffness are considered. The results from the 2-D and 3-D analyses are then used to calculate the live load distribution factors (LLDFs) for the abutments and piles of IBs as a function of the above mentioned properties. The analyses results revealed that using AASHTO LRFD LLDEs result in generally unconservative estimates of live load moment in the abutments. However, AASHTO LRFD LLDEs are found to produce exceedingly conservative estimates of live load shear in the abutments as well as live load shear and moment in the piles.

Effect of Modifying Bearing Fixities on the Seismic Response of Short- to Medium-Length Bridges with Heavy Substructures

The effect of modifying the fixity conditions of the bearings on the seismic response and vulnerability of existing bridges with heavy substructures is studied. For this purpose, nonlinear seismic analysis of a typical bridge with heavy substructures is conducted to assess its seismic response and vulnerabilities. Next, the bearings are modified to obtain four different configurations of bearing fixities over the substructures. Nonlinear seismic analyses of the bridge are conducted to assess its seismic response and vulnerability for each bearing fixity configuration. It is found that changing the fixities of the bearings may be an effective response modification technique to mitigate the effect of seismic forces on vulnerable substructures of the bridge under consideration. The thermal load effects on the bridge with fixed bearings are found to be generally negligible compared to seismic load effects. Thus such a response modification technique may be used for the economical design of new or seismic retrofitting of existing short- to medium-length bridges similar to that considered in this study and subjected to low- to moderate-intensity ground motions.