Ana M. Ruiz-Teran

Structural behaviour and design criteria of under-deck cable-stayed bridges and combined cable-stayed bridges. Part 2: Multispan bridges.

This paper deals with the application of under-deck cable-staying systems and combined cable-staying systems to prestressed concrete road bridges with multiple spans of medium length. Schemes using under-deck cable-staying systems are not suitable for continuous bridges, as they are not efficient under traffic live load and only allow for the compensation of permanent load. However, combined cable-staying systems are very efficient for continuous bridges and enable the design of very slender decks (1/100th of span) where the amount of materials used is halved in comparison with conventional schemes without stay cables. In this paper, the substantial advantages provided by combined cable-staying systems for continuous bridges (such as high structural efficiency, varied construction possibilities, both economic and aesthetical benefits, and landscape integration) are set out. Finally, design criteria are included.

Inelastic Behaviour of RC Members Incorporating High Deformability Concrete

This paper examines the inelastic behaviour of dissipative zones in structural members incorporating high deformability concrete materials in which mineral aggregates are partly replaced by rubber particles. An experimental study on three large-scale circular reinforced concrete column specimens, subjected to lateral cyclic displacements and co-existing axial loads, is described. The testing arrangement, specimen details, and main observations, are presented and discussed. The test results enable a direct assessment of the strength and ductility characteristics of the specimens. In particular, the study permits an evaluation of the comparative performance of structural members with and without rubber replacement, as well as the influence of external confinement. The results show that, in comparison with conventional reinforced concrete members, structural elements incorporating a significant proportion of aggregate replacement by rubber particles can offer a good balance between bending capacity and ductility, particularly for modest levels of co-existing axial loads. For column members required to sustain substantial gravity loads, favourable performance can be achieved in rubberised concrete members by means of strength enhancement through external confinement such as fibre reinforced sheets. Based on the experimental findings, the main material and response parameters are discussed and their influence on the overall structural behaviour are highlighted.

Dynamic behaviour of under-deck cable-stayed bridges under the action of moving loads

Fernando Madrazo-Aguirre, born 1984, received his Civil Engineering degree from the University of Cantabria, Spain. He worked as a Chartered Structural Engineer for Saitec Engineering before joining Imperial College London as a PhD student. Dr Ruiz-Teran received her MEng and PhD from the University of Cantabria, Spain. She worked as Chartered Bridge Engineer for APIA XXI and Arenas & Asociados for several years before becoming an academic. She is currently a Lecturer at Imperial College London. Dr M Ahmer Wadee received his BEng and MSc from Imperial College London, and his PhD from the University of Bath. He has been lecturing at Imperial since 1999, and currently holds the position of Reader in Nonlinear Mechanics. He is a Fellow of the UK Institute of Mathematics and its Applications.

Structural Behavior of Inferior-Deck Spatial Arch Bridges with Imposed Curvature

Spatial arch bridges have significant out-of-plane behavior that must be controlled even under vertical loads. In some designs, the centerline of the arch may not lie within a plane. This study focuses on the structural behavior and the effect of the geometrical configurations of inferior-deck arch bridges with imposed curvature. In this type of spatial arch bridge, the arch and the deck centroid lines are both contained in the same vertical cylinder. The aim of this study is to propose the most appropriate design for controlling the out-of-plane response. A simple analytical model representing the stiffness of the arch, the deck, and a hanger allowed us to determine the main variables that control the behavior of the system. We also analyzed a series of linear three-dimensional-frame finite-element models of the complete bridge. This study demonstrates that nonplanar arches can be approximated by inclined planar arches. These parametric analyses have led to a set of recommended relevant design criteria for such bridges.

Statically-Indeterminate SFRC Columns under Cyclic Loads

The present study is aimed at examining the structural response of steel-fibre-reinforced concrete (SFRC) columns under reversed-cyclic loading, which were investigated by means of non-linear finite-element analysis (NLFEA). The focus was on investigating the potential of steel fibres in compensating for reduction in conventional transverse reinforcement [and thus the spacing between shear links was increased by 50% and 100% while the fibre volume fraction (V f ) was increased to 1%, 1.5%, 2% and 2.5%]. This is useful in situations where the latter is required in significant amounts (e.g. in seismic design) leading to congestion and practical difficulties in placing the links. The critical factor in the seismic response is the cyclic nature of the load, which is examined in the present research work. An interesting feature of the present research work is the consideration of statically-indeterminate SFRC columns, information on which is rare as previous research studies have focused on simply-supported beams. To address this, both indeterminacy and axial loads were considered in the present investigation. Calibration work was carried out using existing experimental data and good correlation was established between numerical and test results. Subsequently, parametric studies were carried out using the practical range of fibre dosages, which provided insight into how the steel fibres can help reduce the amount of conventional shear links.

Investigating the Potential of Using High Performance Concrete in Precast High Speed Rail Bridges

High Speed Railway (HSR) bridges are limited in design by the sudden, heavy, repetitive nature of the vehicle loading. As a result, prestressed concrete HSR bridges are stockier than highway bridges to ensure high mass, stiffness and resistance. Different types of prestressed concrete bridges have been implemented, with a number being constructed using prefabrication techniques. However, the concrete currently used for HSR bridges uses conventional strength levels. Considering the technological improvements that have led to much stronger concretes being available, implementing these into HSR bridges could bring significant benefits.

Comfort in Slender Bridges Subjected to Traffic Loading and Hammering Effects

The verification of the Serviceability Limit State (SLS) of vibrations due to traffic live loads is typically ignored in the design of road bridges with conventional concrete decks. However, the vibrations perceived by pedestrians usually govern the design in slender and light-weight modern structures that take advantage of the improvement in the structural efficiency, material performance and constructive procedures. On the other hand, the comfort of the vehicle users is traditionally ignored in the design of the bridge because pedestrians are usually more sensitive to vibrations. However, in many highway bridges without pathways the only users of the structure are those in the vehicles (drivers and passengers). Considering all the possible bridge users and their specific sensitiveness, this paper addresses the vibration serviceability in a slender under-deck cable-stayed bridge subjected to heavy traffic loading. In this structure the prestressed concrete deck spans a distance of 80 m with a depth-to-span ratio of 1/80. The vehicle-bridge interaction accounts for aspects traditionally ignored like the wheel dimensions and the cross-slope of the bridge. A large number of time-history analyses is conducted to address the influence of road and vehicle properties on the SLS of vibrations. This work is completed with the study of the vehicle impact when it enters and leaves the bridge. The results clearly demonstrate the influence of the wheel dimensions and the road conditions, as well as the importance of high-order modes on the response.