Bridge Structures

One of the determining factors in the design of steel-tied arch bridges is the out-of-plane buckling behavior. While considerable research, focusing on the determination of the geometrical imperfections, using non-destructive testing as well as analytical calculation methods, is available, the influence of residual welding stresses has not been studied in depth. It is assumed that these stresses would have only limited influence on buckling. Still, this paper claims the residual stresses, which are present in the arches, can be of limited importance, since they do influence the out-of-plane shape of the arch. Firstly, a fundamental approach is followed by developing a three-dimensional finite element model of the influence of the welding parameters and weld sequence. In addition, the resulting residual welding stresses are used for an elastic-plastic calculation of an entire arch. This allows for calculating the buckling behavior of arches as realistically as possible.

Following the discovery of discontinuities in a weld specimen, which was made with a process called narrow gap electroslag welding (ESW-NG), the specimen was subject to mechanical cyclical tension loading until failure. The loading involved one block of 100 tension-only cycles at 42 ksi peak stress followed by a second block of 20 tension-only cycles at 55 ksi stress. Phased Array Ultrasonic Testing (PAUT) was performed to understand whether or not the loading protocol has caused the internal discontinuities to increase in length. The PAUT was performed before cycling began and after the end of first block of cycles. Conventional Ultrasonic Testing was also performed in order to develop comparative baseline results. PAUT utilizes an aperture, which is composed of multiple individual small transducer elements which can be pulsed individually at a computer-calculated timing (“phased or delay laws”) producing a sound beam which is swept through a volume of material. Utilizing PAUT, the operator has the ability to “steer” and “focus” the beam electronically through the material being examined at multiple angles in one scan (for example 45° through 75°) in lieu of being fixed at a certain angle as in conventional Ultrasonic testing (UT). The PAUT equipment utilized has the capabilities of 16 active pulsars capable of multiplexing over 64 channels (16:64) displayed in A, B, C, S, Linear scans, or a combination thereof. Scanning with a digital encoder was utilized in order to collect the data for post processing, analysis and data documentation. This presentation will discuss the findings of the PAUT on this weld specimen. The PAUT aperture utilized was a 5L-60 with 1 mm pitch and Sectorial and Linear scans were utilized. The sectorial scan results of the PAUT before and after cycling showed an increase in dimensions of the recorded indications by an average of 6–8 mm or approximately 50% of the original dimensions. The presentation will also include a discussion of the advantages and limitations of PAUT for various bridge applications. The advantages of PAUT include speed, flexibility, and the ability to perform complex inspections.

Pedestrian loading on flexible structures such as footbridges, grandstands and lightweight floors is an area, which is receiving significant attention from the research community of late. One of the key parameters in determining the structural response is the frequency of the bridge.

The authors are currently researching pedestrian-induced loading on flexible structures and also the use of FRP materials in construction. This paper describes the amalgamation of these two discrete research interests by detailing the material testing, design and construction of a laboratory-scale FRP composite footbridge.

The bridge was constructed from glass fibre reinforced polymer (GFRP) composite beams, with GFRP lateral bracing. This structure supports a timber deck. The bridge is lightweight and the span can be altered from 6.5 m to 8.0 m clear span to adjust the structural response, by altering the natural frequency and magnitudes of displacements. The bridge can also be fixed in position through the use of removable intermediate supports. The bridge also has a force plate mounted at mid-span, facilitating direct measurement of the reaction force between the pedestrian and the structure.

This paper presents the results of preliminary walking trials on this bridge in both the fixed and free suspension states, and across a range of spans, allowing analysis of the interaction between pedestrian loading and the structural response of flexible structures.

Vandalism, human errors or severe accidents could result in significant fire events on and beneath bridges. The resulting damages often require a reconstruction of the bridge superstructure or, in case of a complete collapse, of the whole bridge. In a research project well-founded and systematic findings regarding the consequences of extreme fire events beneath and on top of bridges were elaborated. The examined scenarios include solid and liquid fires which were investigated with Computational Fluid Dynamics (CFD) calculations. In order to validate the CFD models used, an original-scale bridge fire test was conducted, using a fire scenario with a truck loaded with wooden pallets. In order to answer the question which bridge structures are the most vulnerable to extreme fire events and have to be protected in the future, especially civil engineering aspects should be taken into account with due consideration given to bridge geometry, clearance, material and structure.