Exterior Span Research Articles

Live load and long-term response of steel bridges with high skew

High skew in bridges alters live load distribution and creates performance issues such as deck cracking, superstructure in-plane (horizontal) displacements and bearing distress. In-plane superstructure displacements, also called racking, are particularly important as they cause misalignments of superstructure and approach slabs, stress bearings and expansion joints. This study had two objectives: to evaluate live load distribution in skewed bridges and to understand how skew influences in-plane superstructure displacements. The effect of bridge design details on live load distribution and in-plane superstructure displacements was assessed through parametric studies on highly skewed bridges.A three-span, steel girder-concrete deck bridge with a 47-degree skew was load tested. Load test results were employed to validate finite element analyses that were used to understand the impact of varying skew angle, bridge features and bearing fixity on live load distribution and in-plane superstructure displacements. The ability of the American Association of Highway and Transportation Officials Load and Resistance Factor Design Bridge Design Specifications (AASHTO LRFD BDS) to accurately capture live load distribution for steel girder bridges was evaluated.Field test results, consisting of girder bending and vertical shear strains measured through strain gages strategically located on one of the exterior spans, and parametric studies showed that AASHTO LRFD BDS predicted shear and moment distribution very conservatively and closely, respectively. Seasonal temperature changes were sufficient to create in-plane (horizontal) superstructure displacements. These displacements caused the superstructure to rotate towards obtuse and acute corners for negative and positive temperature changes, respectively. Larger skew angles led to greater transverse (i.e., perpendicular to bridge longitudinal axis) displacements at girder bearings. Longitudinal (i.e., parallel to bridge longitudinal axis) displacements were consistently smaller than transverse displacements and were not affected by skew. Mixed bearing fixity arrangements, with both fixed and expansion bearings over the same pier, limited superstructure transverse in-plane displacements.

Experimental study of the load-deformation behaviour of the precast post-tensioned continuous girder for straddle monorail: Full-scale load test under service and ultimate loading conditions

This study presented the results of an experimental program conducted on a newly proposed Full-scale Precast Post-tensioned Continuous (FPPC) girder for straddle monorail. The investigated FPPC girder represents the actual size, design and construction details for a newly designed monorail transit system (Yellow Line and Pink Line Monorail) in Bangkok, Thailand. The salient features of the newly proposed girder system include lightweight, low-cost, easy and fast construction. The newly proposed FPPC girder is mainly comprised of three reinforced concrete (RC) hollow haunched girders, four piers or supports, two pier segments, four wet joints, and four bearings at each support. The FPPC girder was constructed at the casting yard of Sino-Thai Engineering and Construction Public Company Limited (STECON), Thailand. The FPPC girder was tested under different loading conditions (such as service and ultimate loading conditions). Both service and ultimate loads were applied as two-point loadings. Service load in a monotonic manner was applied on the right exterior span (two-point), middle span (two-point), and on the left exterior span and middle span (four-point). Meanwhile, the ultimate load in a monotonic manner was applied only on the left exterior and middle span as a four-point loading scheme. The test results indicate that the behaviour of the FPPC girder under service load conditions is elastic. Further, cracking of the concrete was not observed at any location. The observed maximum deflections under service load conditions were less than the permissible limits at all locations. Further, the maximum ultimate load-carrying capacity was observed to be much greater than the design load under ultimate loading conditions. This is an indication that the design details and construction procedure of FPPC girder are appropriate and further that this system could be used effectively to construct straddle monorail transit systems. Finite element analysis of FPPC monorail bridge girder was also performed by using a computer program ATENA which is a computational tool for nonlinear engineering analysis of bridges and culverts. The finite element analysis results indicate that the computer program ATENA is well capable to predict the ultimate load carrying capacity, displacement and cracking patterns of FPPC girder.

Rapid prediction of deflections in multi-span continuous composite bridges using neural networks

This paper proposes closed form expressions for the rapid prediction of deflections in steel-concrete composite bridges of large number of spans subjected to service load. The proposed expressions take into account shear lag effect, flexibility of shear connectors and cracking in concrete slabs. Three separate neural networks have been developed for right exterior span, left exterior span and interior spans. The closed form expressions have been obtained from the neural networks developed in the study. The training, validating and testing data sets for the neural networks are generated using finite element software ABAQUS. The proposed expressions have been validated for number of bridges and the errors are found to be small for practical purposes. Sensitivity studies have been carried out using the proposed expressions to evaluate the suitability of input parameters. The use of the proposed expressions requires a computational effort that is fraction of that required for the finite element analysis, therefore, can be used for rapid prediction of deflection for everyday design.

Ampliación del puente de Los Santos en la A-8 de 12,00 a 24,60 metros, sin cortes de tráfico

This paper describes the main features of the Los Santos Bridge widening project and construction. The bridge is 600m long, with three main spans of 150m and two exterior spans 75m. The original deck width has been increased from 12.00m to 24.60m, in order to bear two new traffic lanes. The widening project is based on the idea of minimizing the strengthening of the original structure, and has therefore implied an enormous challenge, finally solved with remarkable optimizations, some of which are described in this paper.

Full bridge testing at scale constructed with novel FRP stay-in-place structural forms for concrete deck

A system of FRP stay-in-place (SIP) formwork for concrete bridge deck is tested within a full bridge setting, including multiple girders, diaphragms and monolithic connections between components. The 4350×3250mm footprint of the test bridge represents a 1:2.75 scale of a 12.5m span full scale bridge. It includes four simulated precast concrete girders, supported at both ends on neoprene bearing pads with integral concrete end diaphragms. The deck is cast compositely on the girders using a novel configuration of FRP SIP forms, except for a control portion constructed using traditional steel reinforcement. Fifteen tests were carried out to investigate the effects of girder spacing, interior versus exterior spans, end- versus middle-sections, loading on versus loading off splices of FRP panels, FRP surface treatment, and splice method. Results show the FRP SIP form system exceeded code requirements, exhibiting safety factors between 2.8 and 4.3 over factored loads. Location of test pads (interior versus exterior span) had a substantial impact on performance, leading to a difference of up to 32% in capacity, with exterior and edge pads exhibiting the lowest loads. Using adhesive bond at concrete–FRP interface mitigated this reduction. Lack of panel-to-panel splice detailing reduced strength by 21% if loading was between splices, but no reduction occurred when loading was directly above splice.

Integral Abutment Bridge behavior under uncertain thermal and time-dependent load

Prediction of prestressed concrete girder integral abutment bridge (IAB) load effect requires understanding of the inherent uncertainties as it relates to thermal loading, time-dependent effects, bridge material properties and soil properties. In addition, complex inelastic and hysteretic behavior must be considered over an extended, 75-year bridge life. The present study establishes IAB displacement and internal force statistics based on available material property and soil property statistical models and Monte Carlo simulations. Numerical models within the simulation were developed to evaluate the 75-year bridge displacements and internal forces based on 2D numerical models that were calibrated against four field monitored IABs. The considered input uncertainties include both resistance and load variables. Material variables are: (1) concrete elastic modulus; (2) backfill stiffness; and (3) lateral pile soil stiffness. Thermal, time dependent, and soil loading variables are: (1) superstructure temperature fluctuation; (2) superstructure concrete thermal expansion coefficient; (3) superstructure temperature gradient; (4) concrete creep and shrinkage; (5) bridge construction timeline; and (6) backfill pressure on backwall and abutment. IAB displacement and internal force statistics were established for: (1) bridge axial force; (2) bridge bending moment; (3) pile lateral force; (4) pile moment; (5) pile head/abutment displacement; (6) compressive stress at the top fiber at the mid-span of the exterior span; and (7) tensile stress at the bottom fiber at the mid-span of the exterior span. These established IAB displacement and internal force statistics provide a basis for future reliability-based design criteria development.

Optimization of Continuous Post-Tensioned Concrete Bridge Girders of Non-Uniform Depth

Post-tensioned single-cell concrete box girders of variable depth are used in continuous bridges to achieve both economy and aesthetics. In this paper, the minimum prestressing for a given two- or three-span continuous bridge deck profile is achieved through a constrained optimization procedure using linear programming in conjunction with gradient method of optimization. The constrained nonlinear problem is solved by transforming it to a linear one by introducing a new design variable which proportions long (full length) and short tendons. A gradient search technique is used to solve iteratively the optimization problem. The design variables include interior to exterior span ratio (for three-span), the depth profile of the cross-section, tendon profile, and prestressing force. The total cost of the member is taken as the cost of structural materials (concrete and prestressing steel), excluding the cost of formwork. The design constraints are the prescribed limits on the allowable stresses, ultimate strength, and serviceability requirements as per ACI 343R-95. A purpose-built computer program has been developed to readily determine the optimum prestressing for a given bridge deck profile. From solutions of a number of hypothetical bridge girders using AASHTO H20 bridge loading, several useful results related to design are obtained. Results show that for a symmetrical three-span and two-span continuous bridge girder, the optimum prestressing consists of an optimum arrangement of both long and short tendons, and for a three-span girder of prescribed length, the optimum design is attained at an optimum ratio of interior to exterior span with 1.35 to 1.45.

THE EFFECT OF DIMENSIONAL PARAMETERS ON THE BEHAVIOUR OF REINFORCED CONCRETE SLABS WITH CONTINUOUS DROP PANEL

In this study, a reinforced concrete story frame with the slab with continuous drop panel in which slab span length was equal in two directions was investigated. In the finite element modeling, the thickened portions of the slab which was called band-beams or slab-bands were accepted as frame elements and slabs as shell elements. The lumped type plastic hinge model was used for the nonlinear behavior of the story frame system under the dead and live loads. In total, 810 solutions were performed on the story frame by modifying some properties, namely: the concrete strength, the span length, the width of continuous band-beam, the height of continuous band-beam and the percentage of steel reinforcement. The support moments, the span moments and span midpoint vertical deflections were calculated for the interior and the exterior spans. Using these results, several functions of the moment and deflection were obtained by using STATISTICA program. The results obtained using the equivalent frame method and the defined functions were compared with those of the finite element method. It was concluded that the proposed method (defined functions) solutions were more compatible with those of the finite element method according to the equivalent frame method results.

Span ratios in bridges constructed using a balanced cantilever method

This paper introduces a relation to determine the span ratio between exterior and interior spans, which is required in the preliminary design stage of bridges constructed by balanced cantilever method. On the basis of the numerical results obtained by rigorous time-dependent analyses and by the simple equations introduced in the companion paper, the moment distribution along the spans and its variation with the construction sequence are reviewed, and a recommendation for a rational design is suggested. First, a relation for the initial tendon force is derived on the basis of an assumption that no vertical drift occurs at the far end of a cantilever beam due to the balanced condition between the self-weight and the cantilever tendons. In advance, the determination of an effective span ratio is followed with an assumption that the magnitude of maximum negative moment must be the same as that of the maximum positive moment along all of the spans. Finally, many rigorous time-dependent analyses are conducted to establish the validity of the introduced relations, and this paper shows that an effective span length ratio of the exterior span to the interior span ranges between 0.75 and 0.8.

OPTIMUM POST-TENSIONING FOR THREE-SPAN CONTINUOUS SLAB-TYPE BRIDGE DECKS

An optimization procedure is prescribed in this paper to find the minimum prestressing force and the corresponding tendon profile required for three-span continuous slab-type bridge decks using a combination of both long and short tendons. The constrained nonlinear problem is solved by first transforming it into a linear one with the introduction of a new design variable which defines the proportion of long and short tendons. The problem is then solved iteratively by linear programming in conjunction with a gradient search technique. The results show that for a three-span continuous bridge deck with the interior span longer than the exterior one, the optimum prestressing consists of a combination of both long and short tendons. For the three-span bridge of a prescribed length, the procedure determines the optimal ratio of the interior to the exterior span for which the required prestressing force is minimum.

Simplified Equivalent Loads of Prestressing

This paper gives one simple set of equations for the determination of the equivalent loads of prestressing, which not only apply to all possible cases but are also easier to use than existing formulas. They can be used for interior spans, exterior spans, simple spans, and cantilever spans, as well as many other cases. These equations allow for the direct analysis of the effects of prestressing in a plane frame computer program. Since virtually all practicing structural engineers have access to a plane frame program and only need some general way of applying prestressing into the program, they will find these equations extremely useful. An example problem is included. These equations also facilitate the determination of both the vertical component of prestress used in shear calculations and friction losses due to the curvature of the tendon.

Behavioral load testing of the Disraeli facility

The Disraeli facility, which was completed in 1960, consists of several overpasses utilizing rolled steel beam construction and a riveted steel plate girder bridge crossing the Red River in Winnipeg, Manitoba. The total length of the facility is approximately 707 m (2320 ft). In 1984, the City of Winnipeg commissioned Reid Crowther and Partners Limited to perform a load test on the facility to ascertain the possibility of increasing the maximum gross vehicle weight limit. The tests were performed on three consecutive Sundays, from September 23 to October 7, 1984.Three spans were tested. One normal and one skewed span were selected for the overpasses to study possible differences in their behavior along the exterior span of a three-span continuous riveted plate girder bridge over the Red River. The test was designed to determine the structural response of the bridges at different load levels, to determine the load distribution characteristics, and to investigate dynamic impact values for the test vehicles.This paper describes the instrumentation layout, data acquisition system, test vehicles, and testing procedures. Test results and comparisons with the predicted values utilizing conventional analysis are included.