• Structural Engineering and Mechanics
• /
• v.61 no.3
• /
• pp.419-426
• /
• 2017

Recently, the transportation of dangerous explosive goods is increasing, which makes vehicle blasting accidents a potential threat for the safety of bridge structures. In addition, blasting accidents happen more easily when earthquake occurs. Excessive dynamic response of bridges under extreme loads may cause local member damage, serviceability issues, or even failure of the whole structure. In this paper, a new explosion-proof and aseismic system is proposed including cable support damping bearing and steel-fiber reinforced concrete based on the existing researches. Then, considering one 40m-span simply supported concrete T-bridge as the prototype, through scale model test and numerical simulation, the dynamic response of the bridge under three conditions including only earthquake, only blast load and the combination of the two extreme loads is obtained and the applicability of this explosion-proof and aseismic system is explored. Results of the study show that this explosion-proof and aseismic system has good adaptability to seism and blast load at different level. The reducing vibration isolation efficiency of cable support damping bearing is pretty high. Increasing cables does not affect the good shock-absorption performance of the original bearing. The new system is good at shock absorption and displacement limitation. It works well in reducing the vertical dynamic response of beam body, and could limit the relative displacement between main girder and capping beam in different orientation so as to solve the problem of beam falling. The study also shows that the enhancement of steel fibers in concrete could significantly improve the blast resistance of main beam. Results of this paper can be used in the process of antiknock design, and provide strong theoretical basis for comprehensive protection and support of girder bridges.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.24 no.9
• /
• pp.731-740
• /
• 2014

Occupants induced floor vertical vibrations may cause other occupant's annoyance and lead to social loss. To help control such floor vibrations, several criteria have been developed mostly based on human perception tests and floor vibration tests. Floor vibration is evaluated by comparison with criteria and vibration parameters of subject floor, such as frequency, damping ratio, acceleration value, vibration duration time and occurrence frequency. Three acceleration value parameters are used in criteria; peak acceleration, rms acceleration and VDV, when a floor vibration serviceability is evaluated. Meanwhile rms acceleration and peak acceleration are adopted as vibration limit value in criteria and researches of human perception for vibration. Occupants induced floor vibration is transient rather than steady state. However, rms acceleration is not reliable parameter for evaluating transient vibration. The objective of this study is to investigate the characters of human perception level according to acceleration value parameters for vibration induced by heel impacts and walking activities.

• Steel and Composite Structures
• /
• v.9 no.5
• /
• pp.397-418
• /
• 2009

Eight panel specimens were tested in one-way bending to study the behaviour and capacity of composite slab joists consisting of cold-formed steel C-sections and concrete. Various shear transfer mechanisms were implemented on the C-section flange embedded in the concrete to provide the longitudinal shear resistance. Results showed that all specimens reached serviceability limit state while in elastic range and failure was ductile. Shear transfer achieved for all specimens ranged from 42 to 99% of a full transfer while specimens employed with shear transfer enhancements showed a greater percentage and therefore a higher strength compared with those relying only on surface bond to resist shear. The implementation of pre-drilled holes on the embedded flange of the steel C-section was shown to be most effective. The correlation study between the push-out and panel specimens indicated that the calculated moment capacity based on shear transfer resistance obtained from push-out tests was, on average, 10% lower than the experimental ultimate capacity of the panel specimen.

• Structural Engineering and Mechanics
• /
• v.34 no.3
• /
• pp.351-366
• /
• 2010

A novel system identification and structural health assessment procedure of steel framed structures with semi-rigid connections is presented in this paper. It is capable of detecting damages at the local element level under normal operating conditions; i.e., serviceability limit state. The procedure is a linear time-domain system identification technique in which the structure responses are required, whereas the dynamic excitation force is not required to identify the structural parameters. The procedure tracks changes in the stiffness properties of all the elements in a structure. It can identify damage-free and damaged structural elements very accurately when excited by different types of dynamic loadings. The method is elaborated with the help of several numerical examples. The results indicate that the proposed algorithm identified the structures correctly and detected the pre-imposed damages in the frames when excited by earthquake, impact, and harmonic loadings. The algorithm can potentially be used for structural health assessment and monitoring of existing structures with minimum disruption of operations. Since the procedure requires only a few time points of response information, it is expected to be economic and efficient.

• Journal of the Korean Society of Safety
• /
• v.30 no.6
• /
• pp.70-77
• /
• 2015

In this study, the governing design factors of GFRP-reinforced concrete bridge deck are analyzed for typical bridges in Korea. The adopted bridge deck is a cast-in-situ concrete bridge deck for the prestressed concrete girder bridge with dimensions of 240 mm thickness and 2.75 m span length from center-to-center of supporting girders. The selected design variables are the diameters of GFRP rebar, spacings of GFRP rebars and concrete cover thicknesses, Considering the absence of the specification relating GFRP rebar in Korea, AASHTO specification is used to design the GFRP-reinforced concrete bridge deck. The GFRP-reinforced concrete bridge deck is proved to be governed by the criteria about serviceability, especially maximum crack width, while steel reinforced concrete bridge deck is governed by the criteria on ultimate limit state. In addition, GFRP rebars with diameter of 16 mm ~ 19 mm should be used for the main transverse direction of decks to assure appropriate rebar spacings.

• Steel and Composite Structures
• /
• v.38 no.1
• /
• pp.67-78
• /
• 2021

The use of composite beams with partial interaction, with less shear connectors than those required for full interaction, may be advantageous in many situations. However, these beams tend to show higher deflections compared to beams with full interaction, and codified expressions for the calculation of such deflections are not fully developed and validated. Thus, this paper presents a comprehensive numerical study on the deflections of steel-concrete composite beams with partial interaction. Efficient numerical models of full-scale composite beams considering material nonlinearities and contact between their parts have been developed by means of the advanced software ABAQUS, including a damage model to simulate the concrete slab. The FE models were validated against experimental results, and subsequently parametric studies were developed to investigate the influence of the shear connection degree and the coefficient of friction in the deflection of composite beams. The comparison of predicted deflections using reference codes (AISC, Eurocode-4 and AS-2327.1) against numerical results showed that there are still inaccuracies in the estimation of deflections for the verification of the serviceability limit state, according to some of the analyzed codes.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.4 no.1
• /
• pp.11-26
• /
• 1984

The aim of this study is to establish a synthetical optimal method that simultaneously analyze and design reinforced concrete flat slab-column structures involving multi-constraints and multi-design variables. The variables adopted in this mathematical models consist of design variables including sectional sizes and steel areas of frames, and analysis variable of the ratio of bending moment redistribution. The cost function is taken as the objective function in the formulation of optimal problems. A number of constraint equations, involving the ultimate limit state and the serviceability limit state, is derived in accordance with BSI CP110 requirements on the basis of limit state design theory. Both objective function and constraint equations derived from design variables and an analysis variable generally become high degree nonlinear problems. Using SLP as an analytical method of nonlinear optimal problems, an optimal algorithm is developed so as to analyze and design the structures considered in this study. The developed algorithm is directly applied to a few reinforced concrete flat slab-column structures to assure the validity of it and the possibility of optimization From the research it is found that the algorithm developed in this study is applicable to the optimization of reinforced concrete flat slab column structures and it converges to a optimal solution with 4 to 6 iterations regardless of initial variables. The result shows that an economical design can be possible when compared with conventional designs. It is also found that considering the ratio of bending moment redistribution as a variable is reasonable. It has a great effect on the composition of optimal sections and the economy of structures.

• Journal of the Korea Concrete Institute
• /
• v.18 no.5 s.95
• /
• pp.579-588
• /
• 2006

In recent years, the availability of high-strength reinforcing and prestressing steels leads us to build economically and efficiently designed concrete structural members. One of critical problems faced to the structural engineers dealing with these types of structural member is controls of crack width that is used as a criterion for the serviceability in the limit state design. Especially, flexural cracking must be controlled to secure the structural safety and to improve the durability as well as serviceability of the load carving members. The proposed method utilizes the results of pure tension test in which tensile loads are applied both side of specimen, done by Ikki. The bond characteristics of deformed reinforcing bar under pure tension is considered by the area of concrete and rib area. The results of proposed method are compared with the test data and the results show that the proposed method can take into account the dimensions, variation of sectional properties, and direction of reinforcing and gives more accurate maximum bond stress and corresponding relative slip than the existing methods. the characteristics of bonding is considered by using dimensionless slip magnitude and effective reinforcement ratio. The validity of the proposed equation is verified by test experimental data.

• Steel and Composite Structures
• /
• v.35 no.5
• /
• pp.641-657
• /
• 2020

A unique lightweight string truss deployable bridge assembled by thin-walled fiber reinforced polymer (FRP) and metal profiles was designed for emergency applications. As a new structure, investigations into the static structural performance under the serviceability limit state are desired for examining the structural integrity of the developed bridge when subjected to unsymmetrical loadings characterized by combined torsion and bending. In this study, a full-scale experimental inspection was conducted on a fabricated bridge, and the combined flexural-torsional behavior was examined in terms of displacement and strains. The experimental structure showed favorable strength and rigidity performances to function as deployable bridge under unsymmetrical loading conditions and should be designed in accordance with the stiffness criterion, the same as that under symmetrical loads. In addition, a finite element model (FEM) with a simple modeling process, which considered the multi segments of the FRP members and realistic nodal stiffness of the complex unique hybrid nodal joints, was constructed and compared against experiments, demonstrating good agreement. A FEM-based numerical analysis was thereafter performed to explore the effect of the change in elastic modulus of different FRP elements on the static deformation of the bridge. The results confirmed that the change in elastic modulus of different types of FRP element members caused remarkable differences on the bending and torsional stiffness of the hybrid bridge. The global stiffness of such a unique bridge can be significantly enhanced by redesigning the critical lower string pull bars using designable FRP profiles with high elastic modulus.

• Journal of the Korea Concrete Institute
• /
• v.22 no.6
• /
• pp.761-768
• /
• 2010

When cracks occur in reinforced concrete structures, a steel carries all tensile force at crack section, while the concrete between cracks carries a part of the tensile force due to bond, so that the steel is less elongated. This is called the tension-stiffening effect, that plays an important role in verification of a serviceability limit state. But it is a complicated work to use a complex strain distribution between cracks, therefore an average strain is used to calculate deflection and crack width. In Eurocode 2, tension-stiffening effect expressed in the first order form or the second order form is used in calculating an average curvature for deflection. In this study for a flexural member deflection and crack width are calculated using various models for the tension-stiffening effect and the results are compared with the values of Eurocode 2 and KCI provisions. As results, the predicted values using the second order form are appeared to be well agreed with the experimental values and it could secure more analytical consistency.