6.1 Bridge Engineering
Bridge Structure Impact Modelling
Gregoire Labrosse, Andrej Kujikis, J.Geoff Chase, Gregory Cole, Gregory A. MacRae & Geoff W. Rodgers
ABSTRACT: The response of single storey structures subject to earthquake loading in which impact may occur between the structures is investigated. These structures represent bents of a bridge which may have different masses strengths and stiffness and an expansion joint where deformation may occur. The likelihood of increase in response due to impact was quantified in a probabilistic sense for different normalized distances between the structures. The increase of displacement relative to the damage on the structure is computed for ranges of periods. The effect of including a high-force-to-volume (HF2V) lead dissipater between the parts of the bridge is then considered and it is shown that the device does not significantly affect the response in this case.
Seismic Pounding of Bridge Superstructures at Expansion Joints
B. Lindsay, B. Li, N. Chouw & J.W. Butterworth
ABSTRACT: Pounding at bridge expansion joints has been considered as one of the major causes of damage during earthquakes in past decades. Considering the importance of bridges as a lifeline for evacuation and post-disaster rescue works and reconstruction, it is vital to keep bridges intact after an earthquake. The objective of this research was to look at impact models capable of calculating the expected pounding force at bridge expansion joints. The pounding force data recorded was based on a scale model, hence relevant for prediction of damage to real structures. It was found that the Hertz contact model with a non-linear damper has the ability to predict the expected pounding force to a reasonable degree of accuracy. The use of a verified impact model has the potential to provide bridge engineers with useful information about mitigation of pounding damage.
Dynamic Stability and Design of Cantilever Bridge Columns
T.Z. Yeow, G.A. MacRae, V.K. Sadashiva & K. Kawashima
ABSTRACT: In congested metropolitan areas it is often difficult to build bridge columns directly and concentrically below the bridge due to space limitations. Columns with a horizontal cantilever in one direction, forming an inverted "L", are sometimes used. Due to the presence of eccentric loads with this setup, some codes, such as the Japanese Road Association code, require the flexural strength in the direction of eccentricity to be larger than that in the opposite direction by the size of the eccentric moment. However, application of the Hysteresis Centre Curve concept indicates that the strength difference should be doubled for structures with bilinear hysteresis loops. To evaluate the strength difference required, inelastic dynamic time history analyses were conducted using a suite of ground motion records. The columns had different strength differences, periods and capacity reduction factors. The columns were modelled using Takeda and elastoplastic hysteresis loops to observe hysteretic shape effects. From analyses, the optimum strength difference that causes the smallest average residual displacements and the smallest average maximum displacement was found to be 2.5 and 2.3 times the eccentric moment respectively. It is recommended to use 2.5 times the eccentric moment as the strength difference in design.
Design of Linkage Bolts for Restraining Bridge Spans in Earthquakes
J.H. Wood & H.E. Chapman
ABSTRACT: Many New Zealand bridge superstructures consist of simply supported spans, which are interconnected with steel linkage bolts. The main purpose of the bolts is to restrain and prevent the bridge spans falling in an earthquake. The prediction of the forces imposed on the linkages is quite indeterminate because of the many variables that affect the response of adjacent bridge spans during strong earthquake motions. Linkage bolts are therefore designed for a reasonable and practical strength, and are then detailed to yield and have large plastic extensions before failing in tension. The paper presents the results of recent laboratory tensile testing of a range of linkage bar types and conclusions are made regarding the most suitable bar systems taking into account cost, tensile ductility and cold temperature fracture toughness.
Retrofit to Improve Earthquake Performance of Bridge Abutment Slopes
P. Brabhaharan, J. Duxfield, S. Arumugam & G. Gregg
ABSTRACT:
A variety of retrofit techniques have been developed, designed and constructed to mitigate abutment slopes at a number of bridges around New Zealand. These cost effective techniques have relied on a performance based assessment and retrofit design that was adopted for these bridge abutments. Retrofit techniques included ground improvement using drilled stone columns, strengthening using soil nailing and rock bolts and simple buttressing using earth or concrete blocks. These were chosen and tailored to suit the ground conditions and provide the performance appropriate for each bridge. Examples of their application to practical retrofit are illustrated through case studies of their application in New Zealand. Such retrofit contributes to more resilient lifelines, and thus the building of a more earthquake resilient society.
Forced Vibration Testing of in Situ Bridge Span to Determine Effects of Soil-Structure Interaction
L.S. Hogan, L.M. Wotherspoon, S. Beskhyroun & J.M. Ingham
ABSTRACT: Forced vibration testing of an isolated span of the decommissioned SH 20 Puhinui Stream Bridge in Manakau, New Zealand was carried out to capture the response of the span and to determine the effects of soil-structure interaction on the response. The bridge span was four traffic lanes wide, with seven precast concrete columns per pier and supported on precast concrete pile foundations. The span was subjected to shaking along one axis using a large eccentric mass shaker and a benchmark system identification of the unaltered state was carried out. Soil was then removed from around the base of selected columns with a new system identification performed after the alteration to capture the change in mode shapes and natural periods. Forced vibration testing of the bridge was able to capture a 5% increase in natural period for both modes as well as a noticeable reduction in the torsional component of both mode shapes.