M Ogueta-Gutierrez & S Franchini, Universidad Politecnica de Madrid, Spain
Since in 1940 the Tacoma Narrows Bridge was destroyed by the wind, aeroelastic instabilities have been recognized as one of the most challenging aspects of bridge design. They can produce long-term fatigue failure through vortex induced vibrations, or sudden collapse through self-excited flutter. These vibrations may also cause discomfort for the users and temporary closure of the bridge.
Wind tunnel studies are a very helpful tool to understand these phenomena. By means of them, the critical wind speed at which vortex induced vibration and flutter appear can be precisely determined and the design of the bridge can be reconsidered in the early steps of the process.
In this paper, an optimum design of the bridge section is sought. One of the most relevant parameters that influence the stability of a certain deck is the porosity of the barriers. Section model tests have been carried out to find whether an optimum value of the porosity of the barrier exists. This value or range of values must present neither vortex induced vibration nor flutter.
Steel & Iron Bridges
1151
FATIGUE MANAGEMENT OF THE MIDLAND LINKS STEEL BOX GIRDER DECKS
C Hendy, Atkins, Epsom & S Chakrabarti, Consultant UK,
The Midland Links Motorway Viaducts, carrying M5 and M6 around Birmingham, have been subject to a regular programme of assessment, repair and strengthening since 1989 after corrosion problems, primarily due to chloride contamination, were first detected in 1979. A number of the longer spans comprise multiple steel and concrete composite box girders and some of these superstructures are supported by steel box girder cross beams. Assessment showed areas of very high overstress in the web plate at the locations of internal bracings. These overstresses affected ultimate, serviceability and fatigue limit states and arose because of poor detailing of the cross braces and stiffeners.
The greatest concern was the fatigue stresses produced in the web at the end of the transverse stiffeners at the internal bracing locations. This was caused by the distortional stiffness of the bracing coupled with the termination of the transverse stiffener in the web. Acoustic emission sensors were installed to determine if the predicted fatigue activity was actually occurring and elastic shell finite element modelling was undertaken for an improved determination of stresses. Plastic redistribution was considered to demonstrate adequate ULS performance and an analysis was undertaken with potential fatigue damage modelled to prove the structure would not collapse with such damage at the ultimate limit state. In-situ strain monitoring was undertaken both under known test vehicle loading and under normal traffic conditions to derive more accurate fatigue stress spectra. These results were used not only to calibrate the finite element results but also to improve the predicted fatigue life and allow preparation of a long-term strategy for managing and monitoring fatigue activity using a damage tolerant approach.
1183
NEW REPAIR METHOD USING CFRP SHEET FOR CORRODED STRUCTURAL STEEL MEMBERS
D Wakabayashi, Nippon Expressway Research Inst., T Miyashita & M Nagai, Nagaoka Univ of Tech, Niigata, Y Okuyama, Nagano Nat College of Tech, N Koide, Kawasaki Heavy Industries Ltd, Y HIdekuma & A Kobayashi, Nippon Steel, W Horimoto, Kurabo Industries, Ltd, Japan
Loss of cross section owing to corrosion is a primary factor in the deterioration of steel bridges. Therefore, carbon fiber-reinforced plastic (CFRP) has attracted attention as a material for repairing and reinforcing steel bridges because of its light weight, high strength, and superior durability. Although many studies have been published relating to this topic, previous studies have primarily focused on the application of CFRP to axial or bending members. However, most of the corrosion is found on the webs or columns at the ends of the main girders. Few investigations have examined repairing corroded webs or columns using CFRP. In this research, a shear buckling test for steel girders and a uniaxial compression test for cruciform columns are conducted to develop a repair method for corroded steel girder ends using CFRP sheets. In this method, low elastic putty layers are inserted between steel and CFRP sheets to improve the performance of out-of-plane deformation.
G Lagoda, Warsaw Univ of Technology, M Lagoda & T Wierzbicki, Road & Bridge Research Inst. Warsaw, Poland
The paper treats on assessment of the Warsaw Grot Rowecki Bridge across Vistula river renovation design. The bridge after renovation is to carry both local and transit traffic. The main goal of the renovation is adopting the structure to carry five lanes each direction (two for the S type road and three for local traffic) with regard to the claimed loads and government law regulations. Moreover, the bridge will be used by the pedestrian and bicycle traffic.
The steel investigation result analysis, including fatigue aspects, was necessary to assess the designed solution. The structural material ageing was taken under consideration, through the examination steel samples taken from the highest stress amplitudes deck area.
1345
DYNAMIC INTERACTION BETWEEN RAILS AND STRUCTURE IN A COMPOSITE BRIDGE OF 120 M LENGTH
C Jurado Cabanes, Politecina de Madrid, Spain
The new steel composite bridge over Verdugo river for the line of high-speed trains in Galicia (Spain) is has been placed between the localities of Arcade and Pontesampaio. The total length of the viaduct is 120.00 m with a central pillar arranged in the middle of the river, dividing the total length of the bridge in two spans with 60.00 m each one.
The structure consists of a composite deck with two metallic main trusses of 1.80 m of height, on both sides of the platform. The composite slab deck has metallic transverse girders of 0.90 m of height arranged every 5.0 m, where are disposed the pre-slabs, that support the pouring concrete of the deck. The foundation has 6 reinforced concrete piles of 1.75 m of diameter and 21 m of length under the central pillar and 9 of 22 m of length under each abutment.
The project velocity of the line is 200 km/h. Under the rails and over the deck there is ballast and according with the owner, it was needed to study, if it was necessary to dispose expansion devices for the rails.
A 3D finite element model with 7265 nodes, 6569 elements type FRAME and 2003 elements type SHELL has been made, which comprises all the elements of the structure: deck, trusses, girders, central pillar, abutments, mat foundations and concrete piles.
According with the European and Spanish Regulations it is needed to make an extensive model in order to verify three aspects:
Maximum tensions in rails.
Maximum displacements.
Maximum rotations at the ends of spans.
The paper presents all the aspects of the study, compare the different Rules and finally exposes the conclusions.
SH Bun, E Bonet, A Matamoros, C Bennnett, RB Gonzalez, ST Rolfe, Univ of Kansas, Lawrence, KS, USA
This paper is focused on the development of modular shallow trapezoidal boxes fabricated from cold-bent structural steel plate using standard mill plate widths and thicknesses. This concept was developed by a technical working group within the Steel Market Development Institute’s (a business unit of the American Iron and Steel Institute) Short Span Steel Bridge Alliance (SSSBA), led by the current authors. This working group consists of all stakeholders in the steel bridge industry, including mills, fabricators, service centers, industry trade organizations, universities, and bridge owners. The goal was to develop innovative and economical modular solutions for the short-span steel bridge market. The proposed system meets the needs of current industry trends of accelerated bridge construction, while offering an economical solution. This paper will provide an overview of experimental testing currently being conducted and further parametric analysis and design studies focused on assessing behavior and ultimate capacity of the proposed system.
1291
SKEWED STEEL BRIDGES: EFFECTS OF CROSS-FRAME LAYOUT ON FLANGE LATERAL BENDINGS STRESSES DURING CONSTRUCTION
J Zhou, C Bennett, A Matamoros & ST Rolfe, Univ of Kansas, Lawrence, KS, USA
Lateral flange bending stresses can arise from a number of sources, such as wind loading or eccentric concrete placement, but of particular interest are lateral flange bending stresses, fl, that occur due to skew. Lateral flange bending stresses that occur in skewed bridge systems tend to develop due to lateral forces transferred through cross-frames which may connect adjacent girders at different span points. In lieu of a refined analysis, the AASHTO-LRFD Bridge Design Specifications currently permit engineers examining bridges skewed more than 20° to use a minimum value of fl = 10 ksi for an interior girder and fl = 7.5 ksi for an exterior girder. The estimates for fl provided within the AASHTO-LRFD Bridge Design Specifications are based on a limited data set for skewed bridges. Additionally, since the AASHTO-LRFD Design Specifications state that cross-frames or diaphragms should be placed in a staggered configuration when a bridge is skewed more than 20°, the approximate values provided for fl should not be expected to be indicative of the lateral flange bending stresses experienced when cross-frames are instead carried parallel to the skew in bridges skewed beyond 20°. Carrying cross-frames and diaphragms parallel to the skew angle in bridges skewed more than 20° is a practice implemented by some state DOTs, and is primarily done to minimize problems with cross-frame fit-up during erection.
The authors have performed a study to investigate the effects of cross-frame orientation and skew angle upon lateral flange bending stresses, by examining lateral flange bending stresses in a suite of detailed 3D, solid finite element analyses of skewed bridge systems, in which cross-frame layout, spacing, and skew angle were varied. Skewed bridge systems with cross-frames placed parallel to the skew angle as well as systems with cross-frames arranged in a staggered configuration were considered. The models included both material and geometric nonlinearities to assess the lateral flange bending stresses in the different bridge systems.
The findings of this study showed that cross-frames placed parallel to the angle of skew produced significantly lower values for fl than cases in which cross-frames were placed perpendicular to the girder line and staggered. Both reducing the skew angle and decreasing cross-frame spacing were found to reduce lateral flange bending stresses. The values of lateral flange bending stress for all configurations were greater than the bounds of the approximate values suggested by AASHTO. Moreover, the minimum values for fl provided in the AASHTO-LRFD Bridge Design Specifications were found to be significantly lower than the results obtained from this study.
1314
VIBRATION-BASED FE MODELING AND STRUCTURAL ANALYSIS OF THE PADERNO IRON ARCH BRIDGE (1889)
Dr C Gentile & Dr A Saisi, Politecnico di Milano, Italy
The San Michele bridge (1889), one of the most important monuments of XIX century iron heritage, has been studied by Politecnico di Milano since 2009. The first part of the investigation, aimed at the assessing the state of preservation of the historic infrastructure, included preliminary dynamic tests in operational conditions as well as the design and installation (late November 2011) of a continuous dynamic monitoring system in the bridge. More recently, a FE model of the bridge was implemented, and accurate visual inspection and local survey of the corrosion state on the bridge members began, in order to obtain a dynamics-validated model including also the information on the actual local state of preservation of the main structural members of the bridge. After a brief description of the first part of the investigation, the paper describes the FE model, the correlation between the actual dynamic characteristics of the infrastructure and the model prediction, and the results of the numerical calculations carried out to evaluate the effects of present loading conditions.
1341
A PROPOSAL TO INCREASE WELD PENETRATION TO IMPROVE THE FATIGUE STRENGTH OF RIB-TO-DECK WELDED JOINTS IN ORTHOTROPIC STEEL BRIDGE DECKS
V Dung Cao & E Sasaki, Tokyo Inst of Technology, Tokyo, & K Tajima & T Suzuki, Hiroshima, Japan
For rib-to-deck welded joints in orthotropic steel bridge decks, a partial joint penetration with 75% and 80% penetration ratios is required by specifications in Japan and USA, respectively. The effectiveness of the proposed 100% penetration on enhancing the fatigue strength of rib-to-deck welded joints was evaluated by both fatigue tests and finite element analysis using the effective notch stress method. Four full-scale orthotropic deck specimens were subject to laboratory fatigue testing. Each specimen consists of a 12-mm-thick deck plate and one closed 6-mm-thick rib. The rib-to-deck joints of the specimens were fabricated with 75% and 100 % weld penetration ratios. Fatigue test results show that fatigue cracks initiated from the weld toe inside the rib in the 100% penetration specimens, but from weld root inside the rib in the 75% penetration specimens. To investigate this fatigue behavior, strain measurements were taken at 5 mm from the rib-to-deck weld line during the fatigue tests. Results of the finite element analysis indicate that a deeper partial penetration results in a slightly higher effective notch stress at the weld root of the partial penetration weld. The effective notch stress at the crack initiation location with 100% penetration is lower than that obtained with partial penetration. The open angle appears to have a significant effect on the effective notch stress at the upper weld toe inside the rib of the specimens with 100% penetration. An open angle of 1350 at the upper weld toe is a possible recommendation to further improve the proposed weld configuration. The proposed 100% penetration may enhance the fatigue strength of rib-to-deck welded joints.
1299
RESEARCH ON THE NEW CFRP PRESTRESSING SYSTEM FOR METAL BRIDGE STRENGTHENING
TW Siwowski & P Pasko, Rzeszow Univ of Technology, Poland
The use of CFRP prestressed strips in strengthening work has gone through a big development during the past 20 years. It has been revealed that the bending strength and stiffness of steel beams can be considerably enhanced with this technique. The main problem of strengthening with prestressed strips has been the anchor zones. Without mechanical anchorages there have been peeling failures at the ends. Therefore the still development in CFRP strips anchorage systems has been recently observed. The paper briefly describes the research on the new prestressing system for CFRP strips with special steel anchorages. The initial testing has revealed that the concept might be used for strengthening. The steel anchors developed in the frame of the project ensure to sustain the prestressing force up to 70% of the ultimate tensile strength of CFRP strips. The first on-site application of the new system for a composite steel – concrete bridge strengthening is shortly described as well. The presented case study has revealed the effectives of the new prestressing system, which seems to be reliable for steel bridge applications.
IMAGE-BASED INSPECTION SYSTEM FOR ROUTINE VISUAL INSPECTIONS OF UK HIGHWAYS BRIDGES,
S McRobbie & A Wright, TRL, Wokingham, M Burrow, Univ of Birmingham, UK
Concrete overlays of concrete bridge decks are common practice for many transportation authorities and are expected to increase the service life of the underlying concrete deck on the order of 20 years. Nonetheless, many authorities do not permit the overlay to be accounted for in the structural load rating of the repaired deck. This effectively restricts overlays to being relatively thin thereby limiting the utility of overlays as a tool for maintaining a sustainable bridge infrastructure. The authors challenge the assertion that overlays must remain non-structural. The objective of this work is to provide laboratory-based experimental verification and assessment of the performance of reinforced concrete bridge deck slabs rehabilitated by means of hydrodemolition (HD) followed by the application of a latex modified concrete (LMC) overlay. The fundamental objective is to determine whether the overlay may be considered composite with the residual deck and under what conditions composite behaviour may be assumed in eventual load rating of the rehabilitated deck.
Tests of ten full-scale laboratory specimens and four decommissioned bridge slabs (having marked existing damage) are presented. The principal parameter investigated is the depth of HD and subsequent LMC overlay. Depths ranging from 7% to 50% of the original slab depth are considered and, in all but the thinnest cases, the overlay does not increase the overall depth of the slab (an important consideration on existing bridges that must be compatible with existing roadway elevations). Results are considered in terms of overall slab performance including cracking, moment-curvature response and, importantly, behaviour and performance of the LMC-concrete interface. In all cases, LMC-repaired slabs demonstrated analytically-predictable behaviour marginally superior to control monolithic slabs. The results clearly demonstrate that not only is composite action between the overlay and residual slab established and maintained, the interface, when constructed correctly, does not affect slab behaviour.
1196
ANALYSIS OF REINFORCED CONCRETE STRUCTURES USING STIFFNESS ADAPTATION
GMA Schreppers, TNO DIANA BV, Delft, A de Boer, Utrecht, The Netherlands, & D Begg, Univ of Portsmouth
Many bridges in the Netherlands have been built during the 1970’s and as such were not designed for today’s traffic. As a consequence the Dutch Ministry of Infrastructure and the Environment has initiated a program in which existing bridges are inspected and re-examined and in selected cases the load-capacity is assessed by performing numerical analyses. One such bridge is the Heteren Viaduct. The concrete structure is a 17-span double-box girder Rhine Bridge with a length of 974 meters and width of 16.85 meters. During inspection of this viaduct shear cracks were observed in the webs. This bridge has subsequently been analysed using a newly developed “Stiffness Adaptation” method in the DIANA Finite Element program. The method allows the calculation of crack patterns, crack widths and onset of reinforcement yielding. A new and efficient modelling and analysis strategy has also been developed for the assessment. In this strategy a 3D solid model is generated, based on a CAD-model of the bridge. Automatic mesh generating procedures are used so that all details can be modelled in a reasonable time. This paper shows a new approach for both designing and re-assessment of structures using a 3D finite element analysis to perform non-linear analysis using the Stiffness Adaptation method. It can be seen this can be used for very detailed models while significantly reducing run times with improved confidence in the results therefrom.
