Chang-Su Shim

Design of shear connection in composite steel and concrete bridges with precast decks

Abstract For the design of the shear connection in steel–concrete composite bridges with precast decks, design considerations were discussed, and experimental works on the push tests and the bridge model test were performed. The characteristics of the shear connection in a precast deck system are the filling material in shear pockets and the bedding layer between the precast deck and the steel girder. Also, it is necessary to evaluate the structural behavior of the shear connection in case of uniformly distributed shear connectors through experiments. Based on the push tests, the behavior of the shear connection in a precast deck was discussed. In addition, the ultimate strength and the fatigue endurance of the shear connection were estimated. As the thickness of the bedding layer increases, the ultimate strength decreases. The shear load redistribution between shear connectors was verified through the experiment on the bridge model, and shear connectors can therefore be distributed uniformly along the span. Using the experimental results and the finite element analysis based on the partial interaction theory, the shear stiffness of the shear connection and the flexural stiffness of the bridge were evaluated.

Bridge information models for construction of a concrete box-girder bridge

Large construction projects involve collaboration among a large number of participants with different specialised knowledge from various construction processes. A readily accessible bridge information model is needed to enable engineers to innovate prefabricated bridge construction. Three-dimensional (3D) information models can include multi-layered information for different users such as designer, contractor and owner. A construction project life-cycle management system was suggested to integrate and to accumulate valuable information. In this paper, 3D bridge information models for an international concrete bridge construction project were built to integrate design and construction processes. The 3D bridge models were realised by considering work breakdown structure and product breakdown structure to enable digital mock-up and design enhancement and to shorten the learning time of construction engineers. The models were also utilised for the fabrication of precast box segments and for the geometry control during construction. Assessment from the construction director was discussed and additional usage of the bridge information models was suggested.

Cracking of continuous composite beams with precast decks

Abstract Analytical and experimental studies were performed to suggest the design basis for longitudinal prestress of continuous composite bridges with full-depth precast decks. In case of continuous bridges with precast decks, combination of two kinds of prestress should be used to introduce the compression at the joints in negative moment regions, especially the joint area behind shear pockets. Two continuous composite beams with precast decks were tested and their results are presented. Static tests are performed to estimate the behaviour in the elastic range before cracking, to evaluate the reduction of flexural stiffness after cracking and to investigate the inelastic behaviour. Nonlinear finite element (FE) analysis is carried out to compare and to analyze test results. Judging from the test results, the prevention of tensile stress under service loads makes it possible to control cracks at transverse joints. FE analysis shows that additional prestressing after shear connection should be introduced in order to prevent cracking of the deck, and details of precast decks should be carefully designed considering the stress distribution caused by longitudinal prestress.

Experiments on limit state design of large stud shear connectors

For the design of shear connection in high shear areas of steel-concrete composite bridges, large shear studs can be an excellent alternative. Large studs can provide the convenience of removing concrete slab and the proper distribution of shear pockets for precast decks. Through the push-out tests on large stud shear connectors up to 30 mm, which are beyond the limitation of current limit state design codes, static and fatigue behaviors were investigated and comparisons with design equations were performed. Ultimate strength of the shear connection showed that the design shear strength in Eurocode-4 gives conservative values for large studs. Fatigue endurance obtained from the tests was slightly lower than the current S-N curve in Eurocode-4.

Development and Application of Precast Decks for Composite Bridges

This paper deals with prefabricated composite bridges with full-depth precast decks. For steel–concrete composite bridges, a new shear connection and its design provisions were suggested by extensive experiments and finite element (FE) analyses. The shear connection for precast decks was investigated to consider the effects of bedding layer, filling material in shear pockets and group arrangement. For the integrity of the precast decks, longitudinal prestressing was introduced and design guidelines for the magnitude of prestress were proposed. It is necessary to keep the joints compressive during the service life of the bridge to prevent cracking and leakage at the joints. Bonding strength was neglected in the design. In order to take full advantage of precast slabs, the concept of incremental prestressing was adopted for continuous prestressed concrete (PSC) girders. Based on the experimental research on joints and connections, several model tests were performed to verify the suggested design guidelines. There are several applications using precast decks not only for steel bridges and but also for concrete ones. Among them, design characteristics and enhanced details for construction were introduced for two bridges.

Structural performance of composite joints using bent studs

A composite truss bridge is an efficient structural type where the merits of both the steel member and the prestressed concrete member are combined. The design of a connection for the truss bridge is of particular interest due to complex details resulting from concentrated forces at the composite joint. In this paper, experimental investigations were conducted to evaluate the performance of the joint with bent studs welded on a gusset plate. Push-out tests for static and fatigue loadings on a group stud connection were conducted to evaluate the direct shear strength and fatigue endurance of the joint. Because the joints are subject to various loading conditions, flexure-shear tests were also performed to verify the design provisions for the joints under a combination of tension and shear. In order to enhance the structural behavior of the connection, a bent shaped stud was proposed to increase the pull-out strength of the concrete slab. Test results showed that it is adequate to use Eurocode-4 for the evaluation of a shear connection which satisfies the requirement of minimum stud spacing specified in Eurocode-4. Since the shear load is concentrated at the joint structure of composite truss bridges, additional confining reinforcements are needed to enhance the horizontal shear strength of the shear connection. The design provision on the interaction of tension and shear for the joint structure gave conservative results. When the pyramid failure surface was assumed, internal studs had little effect on the pull-out strength of the joint. Constructability of the joint can be enhanced by decreasing the number of connectors and by strengthening the concrete slab through simplified design checks assuming four failure modes and their interactions.

Statistical Properties of Material Strength of Concrete, Re-Bar and Strand Used in Domestic Construction Site

As a fundamental study to introduce the reliability-based design code, a statistical study is conducted for the material strength data collected from domestic construction sites. In order to develop a rational design code based on statistics and reliability theory, it is essential to obtain the statistical properties of material strength. Material strength data for concrete, reinforcing bars, and prestressing strands which are used in domestic construction sites are collected and statistically analyzed. Then, the statistical properties are compared with those used in the process of the reliability-based calibration of internationally leading design codes. The statistical properties of the domestic data are such that the bias factor is relatively uniform between 1.13 and 1.20 and the coefficient of variation is below 0.10. Reinforcing bar data show difference among different manufacturers but there is not much difference among re-bar diameters. In the case of tendons, which are high strength materials, both of the domestic and foreign data show smaller values of the bias factor and the coefficient of variation than those of concrete and re-bar. Statistical distribution of all the material strength can be properly assumed as normal, log-normal, or Gumbel distribution after analyzing the classified data by individual construction site and manufacturer rather than the mixed data obtained from different sources in order to express the individual distribution of each structure.

Effects of Group Arrangement on the Ultimate Strength of Stud Shear Connection

For the design of shear connection for region of highly concentrated shear force in steel-concrete composite bridges, connection details are the most important design issues. Failure modes of the shear connection govern the ultimate strength for the design and governing design parameters can be changed. Instead of rigid shear connectors, this paper deals with the group stud shear connection for the precast decks. Shear pockets for stud connectors arise difficulty in the details of precast decks. Push-out tests were conducted to evaluate the ultimate strength according to the expected failure modes. Main parameters of the test were stud spacing, reinforcement details and stud diameter. Test results showed that current design provisions for the stud connectors can be used for the design of group stud shear connection when the design requirements on the minimum spacing of studs are satisfied and the splitting failure of concrete slab is prevented. An empirical equation was proposed to consider the effect of stud spacing when the spacing is less than the minimum requirement. Fatigue tests showed that the group stud connectors with spacing of more than three times of diameter has similar fatigue life with current design codes. Based on the test results, design recommendations for shear connection in a precast deck bridge were derived.

Enhanced Design Of Precast Concrete Columns By Optimal Axial Steels

Prestressed precast concrete columns are recently considered as excellent design options due to their self-centering capability for seismic actions. Axial prestressing is designed to control cracking at the precast joints by service loads. In this paper, a combination of continuous reinforcing bars and prestressing tendons was suggested to enhance seismic performance as well as economy of precast piers. Cyclic tests were conducted to verify the suggested concept. By preventing buckling and fracture of the reinforcing bars in the plastic hinge region, the test specimens showed remarkable ductility without reduction of their flexural strength. Appropriate magnitude of initial prestressing force was also proposed to prevent fracture of tendons by large lateral deformation of columns in strong earthquakes.

Shake Table Response and Analysis of RC Bridge Piers with Lap-Spliced Steel under NFGM

The near-fault ground motion (NFGM) is characterized by a single long period velocity pulse of large magnitude. NFGM`s have been observed in recent strong earthquakes, Izmit Turkey (1999), Kobe Japan (1995), Northridge USA (1994), etc. These strong earthquakes have caused considerable damage to infrastructures because the epicenter was close to the urban area, called as NFGM. Extensive research for the near-fault ground motion (NFGM) have been carried out in strong seismic region, but limited research have been done for NFGM in low or moderate seismic regions because of very few records. The purpose of this study is to investigate and analyze the effect of near-fault ground motions on reinforced concrete (RC) bridge piers with lap-spliced longitudinal reinforcing steels. The seismic performance of four RC bridge piers under near-fault ground motions was investigated on the shake table. In addition, a RC bridge pier is subjected to pseudo-dynamic loadings. Test results showed that large residual displacements were observed in RC bridge piers under NFGM. RC specimens on the shake table failed at relatively low displacement ductility, compared with the displacement ductility of RC bridge pier subjected to pseudo-dynamic loadings.