Stress Analysis of Rib-to-Deck Joints in Orthotropic Steel Deck Based on Nominal and Effective Notch Stress Approaches

This paper presents the stress analysis of the rib-to-deck (RD) joint in an orthotropic steel deck. Finite element models were developed to evaluate the effects of the wheel load location and weld penetration ratio on the nominal and effective notch stresses at the RD joint. The critical wheel load locations for fatigue-sensitive locations of the RD joint were investigated comprehensively. The potential locations of fatigue crack initiation were evaluated for weld penetration ratios ranging from 0% to 100% at different transverse locations of single- and double-wheel loads. The analytical results indicated that the critical location of fatigue crack initiation was influenced by the weld penetration ratio and transverse wheel load location. An increase in the weld penetration ratio decreased the root notch stress and significantly increased the potential for toe-deck cracking, as the wheel loads were applied at the RD joint and close to the adjacent rib. The nominal stress approach was used to identify the fatigue crack type accurately only for relatively high weld penetration ratios, with the wheel loads applied at the RD joint and over the rib. For the condition of 100% weld penetration ratio with the loads applied at the joint, the fatigue life corresponding to the effective notch stress approach ranged from 66% to 73% of the fatigue life obtained using the nominal stress approach

Experimental and Analytical Studies of Door-Type Modular Scaffolds with Initial Geometrical Imperfections

In the study, the performance and structural behaviors of door-type modular steel scaffolds with different degrees of initial geometrical imperfections were evaluated through experimental and analytical investigations. Two one-story and nine two-story modular steel scaffolds were tested to failure. When the number of stories increased from 1 to 2, a 14.8% reduction in load capacity was obtained for the scaffolds with relatively straight columns. The capacity reduction was mainly due to flexibility at column joints and an increase in the deviation from the vertical alignment. The average capacity reductions increased to 18.9% when the out-of-straightness approached the limit provided by the standards. The effective length factors for capacity calculation were determined. In conjunction with the initial imperfections, the results indicated that the flexibility at column joints and the stiffness of beam and sub-frame elements on modular frames significantly affected the failure mode and ultimate load. The beam and sub-frame elements prevented the buckling failure in the modular-frame plane. Hence, the initial imperfections in the plane of cross bracings were more critical than that of the modular-frame plane, and it is necessary to closely inspect the same while using scaffolds in construction

Monitoring Damage in PC Slabs by Modal and Ultrasonic Tests

The effectiveness of modal and ultrasonic tests for monitoring the damage in precast prestressed concrete slabs was experimentally investigated. Four slabs with two different span lengths and corresponding modes of failure (interfacial shear and flexural failures) were subjected to loading steps until failure. The variations in fundamental natural frequency, damping ratio, ultrasonic pulse velocity (UPV), and ultrasonic wave attenuation in relation to the damage severity and failure mode were investigated and compared. It was observed that the natural frequency was sensitive to flexural crack development. A significant change in the damping ratio was obtained in the slabs with moderate damage. The UPV was not affected by a moderate degree of interfacial shear damage and a low degree of flexural damage; however, it was strongly related to the progression of flexural damage at the severe stage. Among the various indexes, ultrasonic wave attenuation was most sensitive to the development of damage. The method could detect interfacial-shear and flexural cracks at an early stage

Fatigue of Older Bridges in Northern Indiana due to Overweight and Oversized Loads, Volume 2: Analysis Methods and Fatigue Evaluation

This report is the second of a two-volume final report presenting the findings of the research work that was undertaken to evaluate the fatigue behavior of steel highway bridges on the extra heavy weight corridor in Northwest Indiana. The purpose of the study was to evaluate the type and magnitude of the loads that travel along the corridor and then assess the effect of those loads on the fatigue strength of the steel bridges on the corridor. This volume presents the results of an evaluation of the fatigue strength of steel bridge structures along the extra heavy weight corridor. A fatigue load model was developed based on a three-axle and four-axle fatigue truck to accurately represent the fatigue damage caused by the actual truck load history. A fatigue damage model was also developed using a statistical database of resistance parameters to assess the fatigue strength for a level of safety selected by the user. The utility of the model was evaluated through a field investigation of two different bridge structures. Strain data were collected for more than three weeks at both sites. The behavior predicted by two-dimensional and three-dimensional analytical bridge models were compared with measured strain data. It was found that both the 1D and 3D models provided conservative fatigue life estimates, although the 3D model was considerably closer to the measured strain behavior. The fatigue truck along with the fatigue damage model was then used to assess thirteen steel bridge structures along the corridor. A remaining fatigue life of more than 25 years was found for the critical details for all bridges using the most conservative 1D model. Most remaining fatigue lives, however, were considerably longer than 25 years

Fatigue reliability-based analysis methods for the evaluation of steel bridge structures

The objective of this research study is three-fold: to evaluate the accuracy of current available fatigue load models for estimating the fatigue damage accumulation, to investigate alternative procedures in determining bridge responses under truck traffic loadings, and to develop a convenient fatigue evaluation procedure for steel bridge structures. Truck traffic data collected from three different weigh-in-motion sites were simulated and used as input loadings for various analytical bridge models. Fatigue damage accumulations were computed based on Miner\u27s hypothesis and compared with the damage predicted by current available fatigue truck models. The results indicate that fatigue damage can be notably overestimated in short span girders. Accordingly, new 3-axle and 4-axle fatigue trucks were developed. These new fatigue trucks have been shown to more accurately estimate the fatigue damage over a wide range of span lengths. The potential of using traffic count data to estimate the gross weight of a fatigue truck was investigated from an analysis of the vehicle database. The developed statistics for use of traffic count data were compiled with the fatigue reliability concept to predict the fatigue life of two steel bridge structures. The use of traffic count data has been shown to predict cyclic lives relatively close to that predicted using WIM data and a 54-kip gross weight of the AASHTO fatigue truck. Therefore, this concept may be employed as another alternative in the evaluation. Additionally, strain gage data collected at the two structures were decomposed by two cycle counting procedures, one with and one without the racetrack method. The counting results reveal that effective stress ranges produced by the two procedures are not significantly different. This indicates that the racetrack method may be a useful tool to facilitate the counting procedure and significantly reduce the computational time required to predict the fatigue life. Based upon the results obtained from the analysis of a given vehicle database and a parametric study of the fatigue limit state function, an evaluation procedure for the fatigue reliability-based analysis of steel bridge structures was developed. The procedure can be utilized to provide a remaining fatigue life with a prescribed confidence level