AASHTO Provisions Research Articles

Adequacy of Equivalent Static Analysis Method Employing Caltrans, AASHTO, and ATC-32 Provisions in Response Estimation of Vibration-Controlled Bridges

Adequacy of Equivalent Static Analysis Method Employing Caltrans, AASHTO, and ATC-32 Provisions in Response Estimation of Vibration-Controlled Bridges

Longitudinal Multiple Presence of Trucks on Continuous Bridge Spans

In designing and evaluating roadway bridges in the surface transportation infrastructure, truck load is a major variable to account for. For daily operation, truck load also is a primary factor. Trucks on continuous spans were studied, with a focus on their behavior of longitudinal multiple presence in the same lane(s). Current US specifications include provisions for how to account for such multiple presence, and these provisions have evolved over the years. However, the basis for the provisions and their changes have not been well documented. An unprecedentedly large number of high-quality in-motion truck weight data were gathered in eight states across the US and used to investigate trucks’ longitudinal multiple presence behavior. A new approach to analyzing each platoon of trucks recorded in traffic was developed for this purpose. Each random platoon’s total load effect was identified, covering every truck in the platoon, to obtain reliable statistics of the maximum load effects. Results show that longitudinal multiple presence increases with truck volume and span length. Relevant current AASHTO provisions therefore were found to be conservative or overconservative. Accordingly, it was concluded that lower longitudinal multiple presence factor values for evaluation and design are more justifiable. These results may be used by bridge owners and engineers for realistic load rating and design, for more-uniform structural safety and cost effectiveness. This is consistent with the top two goals of the AASHTO Committee on Bridges and Structures’ strategic plan for extending bridge service life and assessing bridge condition.

Investigating the effects of combinations of irregularities on seismic ductility demands and mean response for four-span RC bridges considering displacement direction

The effects of combinations of different types of irregularities have not been studied in details in the past and current seismic design codes do not address this issue appropriately. In this research, 76 regular and irregular bridges with irregularities in both superstructure and substructure were designed and evaluated to investigate the impact of combinations of irregularities on the seismic ductility demands. The irregularity parameters considered in this study include irregularities in span arrangement, different lengths of columns, different abutments support conditions and different stiffness of superstructure. The bridges were designed and checked according to AASHTO provisions. Inelastic time history analysis was conducted using OpenSees software and ductility demands in bridge columns for different bridge configurations were predicted. Predictions of ductility demands were based on the mean responses obtained using a number of ground motion records. Finally, the effect of considering displacement directions in predicting the mean bridge response (i.e., using different methods for predicting the mean response) for irregular and regular bridges was investigated. The results indicate that the combinations of irregularities can significantly increase the ductility demands in some cases compared to the case of regular bridges.

Concrete beam subjected to shear and torsion: a comparison between the Brazilian Standard Code NBR 6118, ACI and AASHTO Provisions

Abstract Most of torsion studies available are relative to pure torsion, arising from the exclusive application of a torsion moment in a concrete beam. This situation, however, is only possible in laboratories. In practice, the vast majority of twisted beams are subjected to the combination of shear forces and torsion, which gives rise to a more complex state of stress to be analyzed. The purpose of this paper is to present the provisions of the ACI 318/2014 Codes, AASHTO and ABNT NBR 6118: 2014 related to shear and torsion, and compare some results with experimental data from Rahal & Collins[3]. It is shown that if the recommended value of 45º is used for θ, the ACI 318/2014 provisions for shear-torsion interaction give similar results compared to ABNT NBR6118: 2014, but these results are very conservative. If the lower limit of 30º is used, the results obtained using both codes departs, and less consistent results are obtained. This paper concludes that using the recommended value of 36º obtained with the AASHTO provisions, some consistent and more accurate results are obtained.

Imaginativeness beyond AASHTO

AASHTO Standard specifications for Movable Highway Bridges has provisions for the use of small diameter sheaves. The provisions are seldom used and may not be understood by most.This paper will discuss the requirements of the AASHTO Movable Bridge Specifications and how small diameter Sheaves can be used n movable bridge applications. This paper will also discuss rope fatigue in general in order to provide some back up as to how and why these provisions were established.This paper will show use the AASHTO provisions for small dimeter sheaves to prepare alternate designs, and the cost of various alternatives will be compared. A preliminary design for Illinois Street Intermodal Bridge will be presented as an example.

Comparative Analysis of Plate Girder Designs In The Composite Bridge Between AASHTO LRFD Bridge Design Specifications 2017 Regulation with SNI 1729: 2015

In the world of construction there are various methods and types of materials used to support the passage of a construction work. One of them is composite girder plate. Composite girder plate is one of the many construction methods that combine two construction materials that are physically different in nature, namely concrete with steel. This type of composite girder plate construction is commonly used for bridge construction work with a fairly large span and width. In its use, of course, it must be preceded by stages of careful planning on a standard and valid basis as well. In the following research will discuss and look for similarities and differences regarding the two types of rules in the planning of composite girder plates, namely the rules of planning composite girder plates using AASHTO LRFD BRIDGE DESIGN SPECIFICATIONS 2017 with SNI 1729: 2015. After doing the initial stages of modeling using CSI Bridge software using the profile cross section constraints of the AASHTO provisions, the internal force obtained is Moment Force (Mu) of 3469.13 kNm and Shear Force (Vu) of 225.98 kNm. Then proceed with the analysis of calculations with the help of Microsoft Excel software namely calculating using the AASHTO LRFD BRIDGE DESIGN SPECIFICATIONS 2017 regulations for stability requirements of strong boundary conditions on the bending requirements. Then a Nominal Moment (ØMn) value of 6420.19 kNm is obtained. Then proceed to calculate the same planning constraints, but this time using SNI 1729: 2015 regulations. Obtained Nominal Moment Value (ØMn) of 6579.88 kNm. Then it can be concluded that the two regulations produce a safe and strong planning, of course in accordance with applicable regulations namely: Moment (Mu <ØMn).

Shear Strength of Dry Joints in Precast UHPC Segmental Bridges: Experimental and Theoretical Research

Precast segmental bridges made of ultrahigh-performance concrete (UHPC) have gained wide research attention and application. The shear transfer of dry joints between UHPC segments is one of the major concerns due to the discontinuity and interruption of the reinforced bars. In this study, direct shear tests of UHPC joints were conducted. Parameters included confining stress, concrete type, joint type, joint shape and number of keys, and arrangement of steel reinforcement. Crack-formation sequences, cracking patterns, ultimate shear load, and vertical slippage were obtained, and typical normalized shear stress–relative displacement curves were calculated. The results show that a higher shear strength of UHPC joints can be achieved with higher confining stress, higher matrix tensile strength, and the addition of steel fibers. Concrete joints with fibers exhibited a limited area of concrete crushing compared with joints without fibers. Large-keyed joints showed a minor increase in shear capacity (9.7%) compared with three-keyed joints. A calculation method for the shear strength of concrete dry joints based on Mohr’s circle was established, and a simplified formula for calculating the shear strength of UHPC dry joints with different compressive strengths was developed. The results of the proposed calculation method were found to agree well with the experimental values. The average ratio of the calculated results to the experimental results was found to be 1.01, with a standard deviation of 0.14. The simplified formula for UHPC joints was also found to have better agreement with the shear test results, with an average ratio of 0.96 and a standard deviation of 0.24, compared with 1.41 and 0.38, respectively, in the AASHTO provisions.

Creep and shrinkage of lightweight self-consolidating concrete for prestressed members

Creep, shrinkage, and prestress losses were measured for lightweight (LWSCC) and normalweight self-consolidating concrete (SCC). A slight expansion was observed for LWSCC at early ages (less than 24 h), but a 100–300 microstrain larger total shrinkage compared to SCC was measured at one year of age for measurements beginning at one day in all environmental conditions. Greater total creep, but a smaller creep coefficient was observed for LWSCC compared to SCC. The creep coefficients at one year for specimens loaded at one day were 2.0 for LWSCC and 2.9 for SCC. Experimentally measured creep, shrinkage, and prestress losses were compared to ACI and AASHTO provisions to assess the suitability of the current provisions for LWSCC.

Development of alternative concrete bridge superstructure systems for short and medium span bridges

Two new concrete bridge superstructure systems for short and medium span bridges are presented. The investigated systems consist of adjacent hollow precast concrete beams with and without concrete topping. The proposed configurations are compared with traditional adjacent box beam and decked bulb tee systems for spans that range from 24.4m to 45.7m. It is demonstrated that the proposed system that features concrete topping (PS2) is lighter than the adjacent box beam system, requires fewer strands, provides shallower superstructure depths, and exhibits lower cambers for spans equal to 24.4m and 30.5m. PS2 addresses the reflective cracking problems manifested in adjacent box beam systems by shifting the location of the longitudinal connections to the bottom flange and away from traffic loads. The system that features no topping (PS4) is slightly heavier than the decked bulb tee system, but features shallower superstructure depths, requires fewer strands, and exhibits lower live load deflections and camber. Transverse bending moments demand in PS4 are reduced compared to the decked bulb tee system due to the smaller span provided by the two web supports. Live load distribution factors (LLDF) for PS2 and PS4 can be conservatively estimated using AASHTO provisions for adjacent box and decked bulb tee systems, respectively.

Analytical investigation of Buckling Restrained Braces’ applications in bidirectional ductile end diaphragms for seismic performance of slab-on-girder bridge

The AASHTO Guide Specifications for Seismic Bridge Design includes provisions for the design of ductile diaphragms as Permissible Earthquake-Resisting Elements (EREs) to resist seismic loads applied in the transverse direction of bridges. However, two major limitations for this system are that: (1) other lateral-load resisting strategies have to be combined with the transverse ductile diaphragms to address seismic excitations acting along the bridge’s longitudinal axis; (2) the existing AASHTO provisions (reflecting the limits of existing research) only apply to straight bridges and provide no guidance on how to implement ductile diaphragms in skew bridges. This paper investigates ductile end diaphragm systems (EDSs) inserted in the slab-on-girder bridge superstructure, with Buckling Restrained Braces (BRBs) arrayed in two different bidirectional configurations so as to provide bi-directional resistance. Benchmark skew and straight bridge models were designed with both EDSs and analyzed using nonlinear time history analysis method to examine their seismic performance. Variations in skew, fundamental period of vibration, and earthquake excitation characteristics were considered. These dynamic analyses allowed investigating the impact of these parameters on global behavior, as well as understanding the magnitude of local demands and the extent of bidirectional displacements that the BRBs must be able to accommodate while delivering their ductile response. The long-term service life of BRBs installed across expansion joints and subjected to bridge thermal expansion histories was also studied and a minimum ratio of the BRB core length over the whole bridge length was recommended. For BRBs’ design and implementation in EDSs, these analytical results can help predict a regime of relative end-displacements representative of the BRB’s demands, when the bridge is subjected to both earthquake and temperature change in the superstructure.

Design expression for web shear buckling of box sections by accounting for flange restraints

This paper presents a new analytical expression for computing the web shear buckling stress with partial flange rotational restraints. The derived expression is suitable to be used in practice for hand calculation and avoids excessive efforts required to perform numerical analysis using finite element or finite strip methods. The material savings resulting from using the proposed design expression are also illustrated. Current design provisions ignore the flange rotational restraints effect in determining the web shear buckling stress for box sections. A comparison is made with AISI, CSA-S16, Eurocode 3 and AASHTO provisions for the limiting conditions. It is also shown that the shear buckling stress may vary by 40% with the current design expressions. Numerical validation of the proposed expression with semi-analytical finite strip method is also presented. The influence of the flange geometric properties on the web buckling stress is also highlighted.

Vertical ground motion influence on seismically isolated & unisolated bridges

In this study, influences of vertical ground motion on seismically isolated bridges were investigated for seven different earthquake data. One assessment of bearing effect involves the calculation of vertical earthquake load on the seismically isolated bridges. This paper investigates the influence of vertical earthquake excitation on the response of briefly steel girder composite bridges (SCB) with and without seismic isolation through specifically selected earthquakes. In detail, the bridge is composed of 30m long three spans, concrete double piers at each axis supported by mat foundations with pile systems. At both end of the spans there exists concrete abutments to support superstructure of the bridge. SCBs which were seismically isolated with ten commonly preferred different lead-rubber bearings (LRB) under each steel girder were analyzed. Then, the comparisons were made with a SCB without seismic isolation. Initially, a preliminary design was made and reasonable sections for the bridge have been obtained. As a result of this, the steel girder bridge sections were checked with AASHTO provisions and analytical model was updated accordingly. Earthquake records were thought as the main loading sources. Hence both cases were exposed to tri-axial earthquake loads in order to understand the effects under such circumstances. Seven near fault earthquake data were selected by considering possession of directivity. Several runs using the chosen earthquakes were performed in order to be able to derive satisfactory comparisons between different types of isolators. Analytical calculations were conducted using well known structural analysis software (SAS) SAP2000. Nonlinear time history analysis was performed using the analytical model of the bridge with and without seismic isolation. Response data collected from SAS was used to determine the vertical load on the piers and middle span midspan moment on the steel girders due to the vertical and horizontal component of excitation. Comparisons dealing with the effects of horizontal only and horizontal plus vertical earthquake loads were introduced.

Anchor Bolt Steel Strength in Annular Stand-Off Base Plate Connections

Anchor bolts in annular stand-off base plates connecting cantilever sign and signal structures to concrete foundations may experience high shear from base plate torsion and direct shear forces. A three-phase experimental study evaluated the steel shear strength of anchor bolts in grouted and ungrouted annular stand-off base plate connections to concrete. Phase 1 included flush-mounted and ungrouted stand-off base plates with ⅝- and 1-in.-diameter bolts loaded in direct shear. Phase 2 employed a novel torsion test approach on 10 circular groups of six ⅝-in.-diameter bolts installed in flush-mounted, ungrouted stand-off, and grouted stand-off base plates, along with three ungrouted groups of three 1-in.-diameter bolts. Phase 3 comprised one ungrouted and three grouted full-scale annular base plate tests of six 1.25-in.-diameter bolts under predominantly torsion loading. Results from this study suggest that AASHTO's provisions allowing bolt bending stresses to be ignored for anchor bolts with an exposed length of less than one bolt diameter overestimate ultimate strength. The beam model suggested by AASHTO accounting for anchor bolt bending fits experimental data well and is recommended for all ungrouted annular stand-off base plates. The American Concrete Institute's 0.8 reduction factor for steel shear strength of anchor bolts in grouted connections was found to be conservative and is also recommended.

Crack Opening Behavior of Concrete Reinforced with High Strength Reinforcing Steel

A major difference between high-strength reinforcing steel and conventional steel in concrete is that the service-load steel stress is expected to be greater. Consequently, the service-load steel strains are greater affecting cracking behavior. A parametric study investigating crack widths and patterns in reinforced concrete prisms is presented in order to establish limits to the service-load steel stress and strain. Additionally, based on the results of available flexural tests, crack widths at service load levels were evaluated and found to be within presently accepted limits for highway bridge structures, and were predictable using current AASHTO provisions. A limitation on service-level stresses of f s ≤ 414 MPa (60 ksi) is nonetheless recommended.

Revisit of AASHTO Effective Flange-Width Provisions for Box Girders

The nonuniform normal stress distribution along the flange of thin-walled flexural members, such as box girders, is recognized as shear lag effects. Effective flange width is widely used to consider shear lag effects in bridge design. The existing provisions for effective flange width in AASHTO LRFD Specifications can be unconservative compared with this study and other design regulations worldwide. An energy-based variation analysis was used in the study to evaluate the AASHTO provisions. With extensive parametric studies, equations were proposed to calculate the effective flange width for box girders. The new provisions consider the critical factors for the shear lag behavior: geometry of the girder, loading pattern, material properties, and the existence of longitudinal stiffeners.

Shear Strengths of Prestressed Concrete Beams Part 2: Comparisons with ACI and AASHTO Provisions

In Part 1 of this paper, an equation for the shear strengths of prestressed concrete beams was developed. New formulas were also proposed for maximum shear strength and for the minimum stirrup requirement. Part 2 of this paper compares the proposed shear design method to the shear provisions in the ACI 318-08 and the 2007 AASHTO LRFD Specifications using 148 test beams. The proposed method is shown to be simpler and more accurate than the ACI and AASHTO specifications, despite the fact that the proposed method does not take into account two variables, prestress force and angle of failure crack, that are involved in the ACI and AASHTO shear provisions.

Unified Flexural Resistance Equations for Stability Design of Steel I-Section Members: Overview

The 2004 AASHTO and 2005 AISC provisions for flexural design of steel I-section members have been revised in their entirety relative to previous specifications to simplify their logic, organization, and application, simultaneously improving their accuracy and generality. This paper provides an overview of these comprehensive developments with respect to the stability limit states. The updated AISC and AASHTO flexural resistances are, with minor exceptions, fundamentally the same. However, the organization in AASHTO facilitates the streamlined design of typical welded I girders. These members are often singly symmetric, have relatively thin webs, may utilize material with smaller yield strengths for the top flange and/or web, and are typically composite in their final constructed condition. Conversely, AISC emphasizes the streamlined stability design of noncomposite nonhybrid compact doubly-symmetric I-section members. This paper highlights the overall continuity of and the fundamental background to the new AISC and AASHTO provisions. The combined AISC-AASHTO rules are presented as a single set of flowcharts applicable for all types of steel I-section members. This comprehensive approach to the design equation developments leads to numerous improvements in the consistency and accuracy of the various specific provisions.

Cyclic Behavior of Single Angles for Ductile End Cross Frames

The cyclic inelastic behavior of single angle braces used in bridge cross frames is described in this paper. Based on the results from experiments, it is shown that steel angles can be designed to achieve a ductile response with large inelastic strains prior to failure under cyclic loading. Preventing fracture in the connections as well as satisfying limiting b/t and Kl/r ratios results in good cyclic behavior and maximum cyclic strains greater than 6%. The tensile yield force for the single angles can be confidently predicted. The buckling capacity is shown to be largely dependent on the effective length of the members which, in turn, is dependent on the type of end condition. Where plastic hinging is expected in the gusset plates an effective length factor of 1.0 can be assumed for the member, while if plastic hinging is expected in the member an effective length factor of 0.7 is appropriate, where the length is defined as the distance between the centroids of the connections. It is recommended that Kl/r for single angles in end cross frames of bridges be limited to 120 to preclude the use of slender members for which the buckling strength is sensitive to effective length. By limiting the slenderness ratio to 120, the members are treated like main members for seismic loads based on AASHTO provisions. The b/t ratio should be limited to those specified for special concentrically braced frames from the AISC Seismic Provisions for Structural Steel Buildings. An analytical model was developed to simulate the nonlinear response of the single angles and a simplified bilinear model was developed for design purposes.

Fatigue and Strength Performance of Concrete-Filled Steel-Grid Bridge Deck

The present paper reports on the results from a series of full-scale experimental tests carried out on concrete-filled steel-grid bridge deck assemblies. The testing focused on assessing the fatigue performance and ultimate strength response of a full-depth-overfilled concrete-filled steel-grid deck configuration. The results from the experimental testing program described herein are compared with the predicted deck responses as per the current AASHTO provisions contained in the LRFD and 16th edition specifications.

Interface Shear in High Strength Composite T-Beams

The purpose of the research reported in this paper was to evaluate the current AASHTO and ACI provisions for horizontal shear strength at the interface of a precast concrete beam and a cast-in-place deck using high strength concrete. The goals were: to extend the provisions for horizontal shear strength of composite beams for use with high strength concrete T-beams; to compare horizontal shear results from beams to shear friction push-off tests using high strength concrete; and, to evaluate current composite beam design provisions for use with high strength concrete beams. The flexure tests and interface failure results indicate that all equations developed previously could be applied to high strength concrete sections used in bridge construction, and the interface shear tests compared well with shear friction push-off tests and demonstrated that the interface shear capacity depends both on the clamping stress provided by the transverse reinforcement and on the concrete strength.