Dynamic Characteristics of a Curved Cable-stayed Bridge:Operational Modal Testing and FE Modeling

This paper summarizes the analytical and experimental dynamic analyses carried out to assess the actual dynamic behaviour of a curved cable-stayed bridge,recently erected in the commercial harbour of Porto Marghera ( Venice,Italy). Ambient vibration tests were carried out to determine the dynamic characteristics of the bridge and more than 20 modes were identified in the frequency range 0～10Hz. In the theoretical study,a 3D FE model of the bridge was developed using an integrated CAD-FEA approach; subsequently,the information obtained from the field tests,combined with simple manual tuning,provided a linear elastic model,accurately fitting the modal parameters of the bridge in its present condition.

Behaviour of a Moment Resisting Composite Steel and Concrete Joint Under Alternate Loading

The authors show the results of a study conducted on a joint connecting a concrete column to a composite steel concrete floor,subjected to tension on the beams as a result of the decomposition of sagging bending moment.The beam to column connection is achieved by means of headed studs welded to the beam and embedded in the concrete cast.Five different configurations have been tested at failure and the results are compared to formulae proposed in literature.Different degrees of ductility,reliability and strength have been obtained varying geometry and reinforcement ratio on the joints tested.

Parametric Analysis on an IAB Superstructure

Integral abutment bridges(IABs) are jointless bridges where the girder or the deck is continuous and connected monolithically to the abutments.A usual and important problem in the design of IABs is how to deal with the soil-structure interaction behind the abutments and next to the foundation piles: this can be considered as a fundamental aspect for the thorough understanding of this type of structures,which requires iterative and nonlinear analysis.In this paper,a 2D simplified finite-element model of a real 400 meters long IAB,built in the Province of Verona-Italy,is implemented and used to perform non linear analysis on the bridge,whose superstructure response is examined in details in the present paper.Then,the results obtained from a parametric study on the IAB,where the soil properties are varied behind the backwall and adjacent to the piles are varied,are described.In the end,a pushover analysis is carried out to assess the failure pattern of the bridge due to temperature change,considered as one of the key parameters in IABs design;finally,the effect of abutment stiffness is also discussed.The case study presented represents the world record for this kind of bridges.Authors believe this can be a cost effective and an efficient strategy to improve the durability and extend the life span of commonly built simply supported flyovers prone to maintenance problems due to bearings and expansion joints durability.

Finite element model updating of a tied-arch bridge using Douglas-Reid method and Rosenbrock optimization algorithm

Condition assessment of bridges has become increasingly important. In order to accurately simulate the real bridge, finite element （FE） model updating method is often applied. This paper presents the calibration of the FE model of a reinforced concrete tied-arch bridge using Douglas-Reid method in combination with Rosenbrock optimization algorithm. Based on original drawings and topographic survey, a FE model of the investigated bridge is created. Eight global modes of vibration of the bridge are identified by ambient vibration tests and the frequency domain decomposition technique. Then, eight structural parameters are selected for FE model updating procedure through sensitivity analysis. Finally, the optimal structural parameters are identified using Rosenbrock optimization algorithm. Results show that although the identified parameters lead to a perfect agreement between approximate and measured natural frequencies, they may not be the optimal variables which minimize the differences between numerical and experimental modal data. However, a satisfied agreement between them is still presented. Hence, FE model updating based on Douglas-Reid method and Rosenbrock optimization algorithm could be used as an alternative to other complex updating procedures.

An innovative steel-concrete joint for integral abutment bridges

Integral abutment bridges are becoming rather common, due to the durability problems of bearings and expansion joints. At the same time, among short- and medium-span bridges, multi-beam steel-concrete composite deck with hot-rolled girder is an economical and interesting alternative to traditional pre-stressed concrete solutions. The two concepts can be linked together to design integral steel-concrete composite bridges with the benefits of two typologies. The most critical aspect for these bridges is usually the joints between deck and piers or abutments. In this paper, an innovative beam-to-pier joint is proposed and a theoretical and experimental study is introduced and discussed. The analyzed connection is aimed at combining general ease of construction with a highly simplified assembly procedure and a good transmission of hogging and sagging moment at the supports in continuous beams. For this purpose, the traditional shear studs, used at the interface be- tween steel beam and upper concrete slab, are also used at the ends of steel profiles welded horizontally to the end plates. To better understand the behaviour of this kind of joints and the roles played by different components, three large-scale specimens were tested and an FE model was implemented. The theoretical and experimental results confirmed the po- tential of the proposed connection for practical applications and indicated the way to improve its structural behaviour.

Nonlinear experimental response of non-conventional composite steel and concrete connection

An experiment was carried out on a set of fullscale specimens of a non-conventional connection between a concrete column and a composite steel and concrete beam defined on the basis of a number of requirements.The proposed connection,conceived in the ambit of semirigid joints,is aimed at combining general ease of construction with a highly simplified assembly procedure with a satisfying transmission of hogging moment at supports in continuous beams.For this purpose,the traditional shear studs used at the interface between the steel beam and the upper concrete slab,are also employed at the ends of the steel profiles welded horizontally to the end plates.The test is aimed at investigating the hogging moment response of the connection under incremental loads until failure.

The optimal shapes of piles in integral abutment bridges

Integral abutment bridges （IABs） can be used to avoid the durability issues associated with bearings and expansion joints. For this type of bridge, the design of the optimal pile foundation, especially with respect to the horizontal stiffness, is a challenging issue. A structural optimization approach is proposed in this paper to optimize the pile foundation shape in integral abutment bridges. A procedure was implemented based on linking MATLAB, where an optimization code was developed, and OpenSees, which was used as the finite element solver. The optimization technique was compared with other techniques developed in previous researches to verify its reliability; the technique was then applied to a real 400 m-long IAB building in Verona, Italy, as a case study. The following two possi- bilities were considered and compared： （a） a pile with two different diameters along the depth and Co） a pile with a pre-hole. In fact, to increase the lateral and rotational flexibilities of the pile head, piles for an integral abutment bridge foundation are often driven into pre- deep holes filled with loose sand. Finally, the case of super-long integral abutment bridges （L = 500 m） with a corresponding displacement on one bridge end of approximately 50 mm was analysed. The following four pile design optimization eases were considered with similar study criteria as the Isola della Scala Bridge： （a） a pinned pile head for semi-integral abutment, Co） a fixed pile head without a pre-hole, （c） a fixed pile head with a pre-hole of any depth, （d） a fixed pile head of a pre-hole with a depth limit （〈 2 m） allowing for enoughembedded length for the friction pile. The case studies confirmed the potential of the proposed optimization techniques for finding the optimal shape of piles in integral abut- ment bridges.