Mark D. Bowman

Fatigue Strength and Evaluation of Double-Mast Arm Cantilevered Sign Structures

Double-mast arm cantilevered sign structures are widely used in Indiana and in many other states. Because of the large sign area and relatively high flexibility, wind loading on these sign structures occasionally produces significant stress cycles. Cracking caused by fatigue damage may occur at several critical spots on the sign structures. An analytical investigation of the fatigue lives of the critical details in double-mast arm sign structures is discussed in this paper. An analytical procedure is introduced, and wind load selection and simulation are explained. Finite element models based on a prototype double-mast arm sign structure are described, and dynamic analyses and fatigue life results are presented. It was found that the post-to-base plate socket weld connection was the most critical detail and that variations in the fatigue life occurred because of differences in the wind environment at various sites.

Multiple Presence Factor for Truck Load on Highway Bridges

Trucks may simultaneously appear on a highway bridge in the same lane or different lanes, which represent the governing load for short- and medium-span bridges. In practice specifications, the multiple presence factor (MPF) to cover these simultaneous loads was developed using in- tuitionormodelswithoutsupportofmeasuredweightdataoftrucksinmotion.ThispaperpresentsaresearcheffortofderivingaMPFbasedonweigh- in-motion(WIM)truck data, forboththestrengthandfatiguelimitstates,includingabout 68milliontrucksgathered for436monthsandfrom 43 sites in California, Oregon, Michigan, and New York. The resulting MPFs are proposed in this paper as functions of bridge-span length, truck-traffic vol- ume, and number of lanes available. They show that the code-specified MPF values are conservative and sometimes overconservative by 400% or more, which may have caused too high requirements for load-rating existing bridges, especially for shorter spans and low truck traffic. The recom- mended MPF may be considered to be adopted in specifications for highway bridge design and evaluation. This paper also presents a new truck-by- truckanalysisapproachforunderstandingtheloadeffectof trucks in motion,takingadvantageof increasinglyavailableWIMdataof largequantityto avoidunsupportedassumptionsinlive-loadmodeling.DOI:10.1061/(ASCE)BE.1943-5592.0000330.©2013 American Society of Civil Engineers. CE Database subject headings: Trucks; Maximum loads; Fatigue; Highway bridges; Design. Author keywords: Truck load; Maximum load; Fatigue load; Highway bridge; Design and evaluation; Multiple presence.

Long-Term Effects of Super Heavy-Weight Vehicles on Bridges

A permit truck which exceeds the predefined limit of 108 kips is defined as a superload in Indiana. This study was conducted to examine the long-term effects of superload trucks on the performance of typical slab-on-girder bridges and to assess the likelihood of causing immediate damage. Typical steel and prestressed concrete slab-on-girder type bridges were analyzed using both beam line analysis and detailed finite element models. Furthermore, one prestressed concrete bridge and one steel bridge were instrumented using more than 50 sensors each. Strains and deflections were measured during a live load test, and each bridge was monitored for more than six months. Capacities of the investigated bridges were calculated and compared with the demands generated by various groupings of typical superload trucks. Analysis of the steel and prestressed concrete bridges demonstrated that typical superload trucks up to a gross vehicle weight of 500 kips are not expected to cause any damage or impair the long term performance of the investigated bridges. Serviceability limit states of the prestressed concrete bridges controlled the rating, and the bridges had adequate strength to accommodate all superloads included in the database. However, strength limit states controlled the rating of steel bridges. Long term monitoring of a continuous and a simple span bridge indicated that strains comparable to those of a 366-kip superload truck can be generated by regular truck traffic. The field measurements also demonstrated that the in-service behavior was different than the design assumptions. Fixity due to integral abutments, effectiveness of the continuity joint in continuous prestressed concrete bridges and contribution of the secondary members lead to notable differences between the expected and the anticipated behavior. Furthermore, the AASHTO girder distribution factor equation was found to be conservative for the investigated bridges. Use of a more accurate method such as FEA or the spring analogy method is recommended for the evaluation of bridges traversed by very heavy superload trucks.

Proposed Method for Determining the Interval for Hands-on Inspection of Steel Bridges with Fracture Critical Members

The proposed assessment procedure presented in this paper may be used to establish inspection intervals for steel bridges with fracture critical members (FCMs) (if adopted by the Federal Highway Administration). The procedure proposed herein only applies to FCM inspections which are defined as follows: a hands-on inspection of a FCM or member components that may include visual and other nondestructive evaluations. The method is rather simple and provides an alternative procedure to the pure calendar based inspection methodology currently specified in the Code of Federal Regulations for all FCMs. There are only two requirements which must first be satisfied in order to use the assessment. The first is that the routine 24-month inspection must continue to be performed on the bridge under evaluation. The second is that a FCM inspection must be performed on the bridge or the FCM under evaluation prior to the implementation of the resulting inspection intervals given from this assessment. The “initial inspecti...

Fatigue Strength and Evaluation of Sign Structures. Volume I: Analysis and Evaluation

This report is a two-volume final report presenting the findings of the research work that was undertaken to evaluate the fatigue behavior of sign structures and, based on that evaluation, to recommend an inspection plan that can be effectively used to detect and minimize possible deterioration due to wind induced loadings of sign structures. The study included a number of signs that are commonly used in Indiana: single-mastarm and double-mastarm cantilever sign structures, box-truss sign structures, tri-chord sign structures, and monotube sign structures. Sign structures with typical dimensions and details were selected as prototypes for each of the various types of sign structures in the study and were subjected to various wind loading environments. The predicted fatigue behavior of the sign structures was used to identify the types of signs and the structural details that were most susceptible to fatigue damage. This information was used to develop an inspection guideline that provides information on where to look during an inspection for fatigue damage. An inspection plan was formulated by using a crack propagation analysis to evaluate crack growth under the most critical wind loading environment. Based on these analyses, an inspection period of four years was recommended for single and double mastarm cantilever sign structures (Class A) and an eight year inspection cycle was recommended for box-truss, tri-chord, and monotube sign structures.

Analysis and Instrumentation of a Steel Bridge for Investigation of Superload Effects

The number of superload trucks, which often carry loads three to 15 times those of common design vehicles, has increased in recent years. The increased frequency of occurrence has prompted concerns about the ability of highway bridges to accommodate such loads and remain in serviceable condition. To address these concerns, an analysis of effects of superloads has been conducted for a case study bridge. A detailed finite element (FE) model of the bridge, including all primary and secondary members, was created to evaluate the behavior. The FE analysis results were compared with results from a controlled load test of the bridge. The girder distribution factors determined experimentally and analytically were found to be significantly lower than comparable design values. Furthermore, from the load tests, the rotational restraint at the girder ends due to the abutments was determined to be as high as a fixed support. The FE model was then used to predict the effects of various superload trucks. The analysis results and field data suggest that some of the stiffener plates and cross-frame members of the analyzed bridge would be overstressed by certain superload truck configurations.

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

This report is the first 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 truck 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 bridge structures on the corridor. This volume presents the results of the experimental field study conducted to evaluate the load and load effects on one steel bridge structure on the corridor. A weigh-in-motion (WIM) system was installed near the bridge structure to evaluate the loads that would cross over the bridge being monitored. Strain values were monitored on two spans of the ten-span continuous bridge being evaluated. Comparisons were then made between strain measurements in particular girders and strain values predicted using the measured truck axle weights. The WIM data indicated that 15% of the Class 9 trucks and 26% of the Class 13 trucks travel heavier than their respective legal limits. Extreme weights of more then 200,000 lbs were observed. In spite of the heavy truck loads being carried, it was found that less than 1 percent of the trucks induce a strain range that exceeds the variable amplitude fatigue limit of the fatigue critical details in the structure being monitored. Lastly, it was found that three-dimensional analytical models provide the best agreement between predicted and measured strain values in the bridge

FATIGUE BEHAVIOR OF BEAM DIAPHRAGM CONNECTIONS WITH INTERMITTENT FILLET WELDS: PART I, VOLUME 2: LABORATORY FATIGUE EVALUATION

This report is the second of a two-part, three volume final report presenting the findings of the research work that was undertaken to evaluate the behavior of Indiana highway bridges with diaphragm members welded directly to the web of the primary beams and girders. Fatigue cracks have been observed at several bridges that utilize the welded diaphragm connection. The seriousness of the cracking and the corresponding potential risk on the integrity of the bridge superstructure were assessed. Inspection and repair guidelines for bridges with the welded diaphragm connections were also developed as part of the research effort. This volume presents the results of laboratory fatigue tests that were conducted to evaluate the cyclic life of staggered and non-staggered diaphragm connections. The performance of three different repair and retrofit procedures on the cyclic life of the welded diaphragm connection was also studied. Analytical models of the cracked diaphragm connection were developed to study the expected response under field loading conditions. Recommendations for implementation of inspection, repair, and retrofit procedures are presented.

Fatigue strength of girders with tapered cover plates

This report contains results from a study to determine the fatigue strength of steel beams with welded partial-length cover plates. Results of an experimental investigation that examined the fatigue strength of various cracked cover plate end details that were subsequently repaired are presented. The repair methods investigated included a slip-critical bolted splice plate connection, air-hammer peening, and a combination of the previous two called a partial bolted splice connection. Also, an analytical model was developed to predict the fatigue behavior of a cover plate end detail that is repaired using one of the three repair methods investigated and which contains a fatigue crack of a known size. The results of both the experimental and analytical studies indicate that a tapered cover plate detail can be effectively repaired with a corresponding improvement in the fatigue resistance.

Evaluation of effects of super-heavy loading on the US 41 bridge over the White River.

Over a period from August 2009 to August 2010 a series of nearly one hundred super-heavy loads ranging in weight from 200,000 lbs to up over 1,000,000 lbs crossed the northbound superstructure of the bridge. The loads were moved to support the construction of a new power plant facility located in Edwardsport, IN. It was unknown what effect this number of super-heavy loading events, over a relatively short period, would have on the long-term performance of the US-41 White River Bridge. Therefore, long-term remote monitoring was used to quantify any negative effects due to the series of superloads. Five primary tasks were undertaken as part of this study: