Multicolumn Bents Research Articles

Risk-based seismic design of diagonal self-centering shape-memory alloy wire-based bracing system in multi-column bent bridges

In this paper, a risk-based seismic design method for diagonal self-centering braces (SCB) with shape memory alloy (SMA) wires implemented in multi-column bents is proposed to enhance the performance of older concrete bridge classes. An existing SMA-SCB system that improves the performance of older reinforced concrete building frames was adopted to numerically examine further applications to nonductile bridges. To this end, risk-based seismic design of the SMA-SCB to minimize the probability of collapse and demolition of bridge classes was developed by adopting a sophisticated finite element model that reflects the recentering behavior of an actual SMA-SCB; probabilistic bridge models considering uncertainties associated with the material and geometrical properties of bridges; refined failure condition; and the total probability theorem. A comparison of the results of the traditional seismic fragility-based and proposed designs indicated that the amount of SMA-SCB required by the former is nearly half of that required by the proposed approach because the traditional approach overemphasizes the demand at larger ground motion intensities.

Seismic assessment of tall pier bridges with double-column bents retrofitted with buckling restrained braces subjected to near-fault motions

Previous researches on dynamic performance of tall pier bridges generally focus on those composed of single columns, and studies on those with double- or multi-column bents are limited. This paper investigates the seismic responses of typical tall pier bridges with double-column bents, as well as the efficiency of mitigating dynamic demands using buckling restrained braces (BRBs). Near-fault motions are specifically considered as input, which might be most devastating loadings for structures with long fundamental periods as tall pier bridges. Nonlinear time history and fragility analysis methods are employed assessing the performance in deterministic and probabilistic manners, respectively, to provide more comprehensive insights. The results show that the BRB could effectively reduce the seismic vulnerability and improve the performance of the prototype bridge, whether linear or nonlinear response is involved. Furthermore, while reducing local excessive seismic demands, the BRB device has little influence on the global responses. This phenomenon is of great significance that it helps engineers to make a quick decision about the location of BRBs, and thus facilitates the retrofitting procedures.

Probabilistic Performance Assessment of Retrofitted Horizontally Curved Multi-Frame RC Box-Girder Bridges

Bridge horizontal deck curvature and the prevalence of in-span hinges in multi-frame RC box-girder bridges have reinforced this class of bridge to response with unique dynamic behavior during seismic excitations. This paper assesses the impacts of 10 different retrofit strategies on the vulnerability of curved multi-frame RC box-girder bridges with multi-column bents based on nonlinear time history analyses in OpenSEES. Consistent with HAZUS-MH definitions, fragility curves corresponding to four damage states at the component and system levels are developed for various bridge deck radii. The results indicate that combinations of retrofit strategies should be used to enhance the desirable level of bridge performance. Moreover, the most effective retrofit strategy in reducing probable damage for a given intensity is dependent on the bridge deck radius and is a function of the damage state of interest.

Enhancing Shear Strength of Capbeam–Column Joints in Existing Multicolumn Bent Bridges Using an Innovative Method

AbstractNonintegrated multicolumn bents are the common type of substructure in existing bridges. Among all possible seismic defects in their behavior, capbeam–column joint behavior has not properly been acknowledged so far. Although for other defects some retrofit methods are available, there are only a few methods proposed for improving the shear strength of these joints. The purpose of this research was to assess the cyclic response of such bents and suggest a practical retrofit method for improving joint behavior without significant damage. To this end, a ¼-scale two-column bent, representative of existing bridges built before 1990, was tested. Using test results, a passive retrofitting method based on the increasing shear strength of joints was developed. The performance of the proposed method was examined on a new specimen similar to the first one. The results show that, unlike the reference bent, which was damaged extensively in joint regions, the joints in the retrofitted specimen did not suffer an...

Probabilistic Vulnerability Assessment of Horizontally Curved Multiframe RC Box-Girder Highway Bridges

AbstractNumerous concrete box-girder bridges in California are horizontally curved and also have at least one in-span hinge. The curvature and in-span hinges in multiframe bridges lead to significant differences in bridge dynamic response during seismic excitations. In this article, a set of analytical fragility curves for horizontally curved highway bridges are developed based on nonlinear time history analyses in OpenSEES, focusing on subclasses of seismically designed multiframe concrete box-girder bridges with multicolumn bents and seat type abutments. Component damage levels are explored for joint seals, columns, bearings, abutments, unseating of decks, foundations, and shear keys, and system level damage states consistent with HAZUS-MH definitions. Curvature was identified to be an important factor that adversely affects the fragility of multiframe bridges. Median value modification factors are proposed to scale fragility curves to account for the deck radius effects.

Performance assessment of multi-column bents with extended pile-shafts under lateral earthquake loads

Under lateral earthquake loads, bridges supported by multi-column bents with extended pile-shafts may be subjected to a large curvature demand at the critical sections with potential for damage. The severity of local damage may however be controlled during design by limiting the curvature ductility demand in the potential plastic hinge region. In this paper, an analytical model capable of assessing the lateral strength and ductility demand of extended pile-shafts with top fixity is proposed. The curvature ductility demand depends on the strength and stiffness of the soil-pile system, as well as the location and length of equivalent plastic hinges. The model allows the severity of local damage in the pile-shafts to be assessed for a wide range of pile and soil properties, and is therefore useful in performance-based engineering. Illustration of the model is made using the Struve Slough Bridge, which collapsed during the 1989 Loma Prieta Earthquake. Results indicate that the bridge failure was initiated by ...

Improving Standard Bridges with Attention to Cast-in-Place Substructure

This paper focuses on improving the efficiency and aesthetics of standard highway bridges with attention to cast-in-place substructure design. Standard short- and moderate-span bridges are predominantly functional and nondescript. Recent developments in superstructure design have led to improved efficiency of construction and material use, with a resulting slender, attractive appearance. However, typical substructure design remains a component where creativity can be played out for considerable improvements to the overall bridge appearance. A review of current cast-in-place substructure systems is presented including individual, wall, hammerhead, and multicolumn bents. Design recommendations for improving overall bridge appearance and the efficiency of the substructure are presented. Attention is given to integrating aesthetics with material and construction efficiency and with economic considerations. Recommendations include addressing structural expression, visibility through the bridge, shaping of the ...

Seismic retrofit of existing highway bridges in Japan

This paper presents the current technical developments for seismic design and seismic retrofit of existing highway bridges in Japan. At first, the histories of the past seismic design codes, past seismic evaluation investigation, and past seismic retrofit practices for highway bridges are described. Then the damage caused by the 1995 Hyogo-ken Nanbu Earthquake and the lessons learned from the earthquake are briefly described. Finally, the seismic retrofit program after the Hyogo-ken Nanbu Earthquake is described with emphasis on research and development as well as field practice of the seismic retrofit of existing reinforced concrete highway bridges such as single column bent, wall-type pier, and multicolumn bents.