Chul-Hun Chung

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.

LOCAL COLLISION SIMULATION OF AN SC WALL USING ENERGY ABSORBING STEEL

This study evaluates the local damage of a turbine in an auxiliary building of a nuclear power plant due to an external impact by using the LS-DYNA finite element program. The wall of the auxiliary building is SC structure and the material of the SC wall plate is high manganese steel, which has superior ductility and energy absorbance compared to the ordinary steel used for other SC wall plates. The effects of the material of the wall, collision speed, and angle on the magnitude of the local damage were evaluated by local collision analysis. The analysis revealed that the SC wall made of manganese steel had significantly less damage than the SC wall made of ordinary steel. In conclusion, an SC wall made of manganese steel can have higher effective resistance than an SC wall made of ordinary steel against the local collision of an airplane engine or against a turbine impact.

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.

STRUCTURAL TEST AND ANALYSIS OF RC SLAB AFTER FIRE LOADING

In the present study the behavior of fire and the residual strength of fire-ignited RC slabs are investigated by experimental tests and numerical simulations. The fire tests of RC slabs were carried out in a furnace using the ISO 834 standard fire. The load capacity of the cooled RC slabs that were not loaded during the fire tests was evaluated by additional 3 point bending tests. The influence of the proportion of PP (polypropylene) fibers in the RC slabs on the structural behavior of the RC slabs after the fire loading was investigated. The results of the fire tests showed that the maximum temperature of concrete with PP fiber was lower than that of concrete without PP fiber. As the concrete was heated, the ultimate compressive strength decreased and the ultimate strain increased. The load-deflection relations of RC slabs after fire loading were compared by using existing stress-strain-temperature models. The comparison between the numerical analysis and the experimental tests showed that some numerical analyses were reliable and therefore, can be applied to evaluate the ultimate load of RC slabs after fire loading. The ultimate load capacity after cooling down the RC slabs without PP fiber showed a considerable reduction from that of the RC slabs with PP fiber.

Evaluation of Seismic Performance of Prefabricated Bridge Piers with a Circular Solid Section

Fast bridge construction has been increasingly needed according to the changed construction environment. This paper deals with quasi-static tests on precast piers for bridge substructures. One of the most crucial aspect of the design of precast prestressed concrete bridge piers is the seismic performance. Seven precast pier elements were fabricated. The amount of prestressing bars, the prestressing force, and the location and number of the joint between segments were the main test parameters. Test results showed that the introduced axial prestress made the restoration of the deformation under small lateral displacement and minor damage. However, there was no effect of the prestress when the plastic hinge region was damaged severely due to large lateral displacement. Judging from the observed damage, the design of the joints in precast piers should be done for the first joint between the foundation and the pier segment. The amount of the necessary prestressing steel may be designed to satisfy the P-M diagram according to the service loads, not by having the same steel ratio as normal RC bridge piers. In order to satisfy the current required displacement ductility, it is necessary to have the same amount of the transverse reinforcements as RC piers. As the steel ratio increases, the energy absorption capacity increases. The number of joints showed a little influence on the energy absorption capacity.

Inelastic Behavior of a Continuous Composite Box-Girder Bridge with Prefabricated Slabs

For the construction of open-topped steel box girder bridges, prefabricated concrete slab could offer several advantages over cast-in-situ deck including good quality control, fast construction, and elimination of the formwork for concrete slab casting. However, precast decks with unreinforced joints should be designed to prevent the initiation of cracking at the joints, because the performance of the joint is especially crucial for the integrity of a structural system. In this paper, experimental results on a 20m-20m continuous composite bridge model with precast decks are presented. Internal tendons and external tendons were used to prevent cracking at the joints. Judging from the inelastic behavior of the bridge model, external prestressing in negative moment regions could offer better performance in terms of cracking and flexural stiffness. Simple plastic analysis was carried out to estimate the ultimate flexural capacity of the continuous bridge, and the incremental prestress of external cables after cracking was estimated.

Evaluation on Structural Performance of Joint with Asymmetric Ribbed Connection Details used in Precast Bridge Deck

A precast concrete deck system is considered an effective alternative in terms of its rapid construction and quality assurance than cast-in-place concrete deck. In precast concrete deck system, structural performance and serviceability are mostly determined by the connection methods between the precast decks. This research proposes more improved precast deck system with asymmetric ribbed connection details improving the disadvantage of previous precast deck system such as difficulties in assembling precast decks. And in this precast deck system, a separate form is not required at the site because partition wall of the precast decks serves as a form when placing non-shrinkage mortar in the connection part of the precast decks. Therefore, rapid construction is possible. Flexural performance is verified through load tests considering main parameter such as rib length in the precast deck connection. From the test results, it can be inferred that the development of the rebar and prevention of adhesion failure in the partition wall of the precast deck system are important factors in securing the flexural performance. Although the structural performance of the precast deck system with asymmetric connection details is gradually reduced as the rib length in the precast deck connection increases, the proposed precast deck system shows sufficient flexural performance and can be applied to the connection part of precast decks effectively.

Assessment of Impact Resistance Performance of Post-tensioned Curved Wall using Numerical Impact Analysis

Abstract In this study, the effect of wall curvature and post-tension force on impact resistance is evaluated by numerical analysis method. A total of twelve cases with two parameters such as wall shape of flat and curved, and consideration of post-tensioning force were included in this study. A 3D detailed finite element model of commercial passenger plane engine is utilized as projectile. The depths of penetration and central displacement calculated from the numerical simulations were compared and analysed. As the results of the numerical simulations of this study, penetration depth was reduced approximately 60∼80% due to the application of post-tension force, but the decrease of maximum central displacement was not remarkable. Also, the effect of curvature was relatively insignificant. Keywords :impact resistance, impact analysis, curvature, post-tension, penetration depth, maximum displacement † Corresponding author: Tel: +82-31-8005-3511; E-mail: jwhee2@dankook.ac.krReceived November 2 2015; Revised November 9 2015;Accepted November 10 2015Ⓒ2016 by Computational Structural Engineering Institute of KoreaThis is an Open-Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License(http://creativecommons. org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Behavior of a CFT Truss Girder with Precast Decks under Negative Bending Moment

For the fast construction of bridges, it is necessary to design bridges as light and modular superstructures. For this purpose, a new composite bridge constructed by segmental method is suggested, which consists of concrete filled steel tubular girders and prefabricated concrete decks. This paper presents a study of the structural behavior of the proposed concrete filled tube (CFT) truss girder at a continuous under negative bending moment. A numerical analysis is performed to verify the structural behaviors of CFT truss girder in continuous support. Based on the results of a numerical analysis, a model with a continuous composite member shape is fabricated and static tests are conducted.

Axisymmetric Modeling of Dome Tendons in Nuclear Containment Building I. Theoretical Derivations

Prestressing tendons in a nuclear containment building dome are non-axisymmetrically arranged in most cases. However, simple axisymmetric modeling of the containment has been often employed in practice to estimate structural behavior for the axisymmetric loadings such as an internal pressure. In this case, the axisymmetric approximation is required for the actual tendon arrangements in the dome. Some procedures are proposed that can implement the actual 3-dimensional tendon stiffness and prestressing effect into the axisymmetric model. Prestressing tendons, which are arranged in 3 or 2-ways depending on a containment type, are converted into an equivalent layer to consider the stiffness contribution in meridional and hoop directions. In order to reflect the prestressing effect, equivalent load method and initial stress method are devised and the corresponding loads or stresses are derived in terms of the axisymmetric model. In a companion paper, the proposed schemes are applied into CANDU and KSNP(Korean Standard Nuclear Power Plant) type containments and are verified through some numerical examples comparing the analysis results with those of the actual 3-dimensional model.