• Journal of the Korean Society of Safety
• /
• v.13 no.4
• /
• pp.292-299
• /
• 1998

In this study, the size effect in flexural and shear behaviors of reinforced concrete beams with stirrup has been studied. The specimens of different size with same longitudinal reinforcement ratio are tested. The major variables of test include the size(relative depth) of the members as well as the longitudinal reinforcement ratios. The nominal resistances in flexure and shear are obtained for various sizes and steel ratios. It is found from the present study that the size effect is also very pronounced for the flexural resistance in reinforced concrete structures. The prediction formulas for the size effect of reinforced concrete beams in flexure and shear are proposed. The proposed equations agree relatively well with experimental data. The present study will provide useful bases for more accurate analysis and design of reinforced concrete structures.

• Structural Engineering and Mechanics
• /
• v.61 no.5
• /
• pp.577-592
• /
• 2017

A computing procedure is presented to predict the ultimate behavior of prestressed beams under torsion. This computing procedure is based on an extension of the Variable Angle Truss-Model (VATM) to cover both longitudinal and transversal prestressed beams. Several constitutive relationships are tested to model the behavior of the concrete in compression in the struts and the behavior of the reinforcement in tension (both ordinary and prestress). The theoretical predictions of the maximum torque and corresponding twist are compared with some results from reported tests and with the predictions obtained from some codes of practice. One of the tested combinations of the relationships for the materials was found to give simultaneously the best predictions for the resistance torque and the corresponding twist of prestressed beams under torsion. When compared with the predictions from some codes of practice, the theoretical model which incorporates the referred combination of the relationships provides best values for the torsional strength and leads to more optimized designs.

• Advances in concrete construction
• /
• v.8 no.2
• /
• pp.145-154
• /
• 2019

The present experimental study addresses the structural response of reinforced concrete (RC) beams strengthened in shear. Thirteen RC beams were divided into four different sets to investigate the effect of transverse and longitudinal steel reinforcement ratios, concrete compressive strength change and orientation for installing carbon fiber-reinforced polymer (CFRP) laminates. Then, we employed a shear strengthening solution through externally bonded reinforcement in grooves (EBRIG) and externally bonded reinforcement (EBR) techniques. In this regard, rectangular beams of $200{\times}300{\times}2000mm$ dimensions were subjected to the 4-point static loading condition and their load-displacement curves, load-carrying capacity and ductility changes were compared. The results revealed that using EBRIG method, the gain percentage augmented with the increase in the longitudinal reinforcement ratio. Also, in the RC beams with stirrups, the gain in shear strength decreased as transverse reinforcement ratio increased. The results also revealed that the shear resistance obtained by the experimental tests were in acceptable agreement with the design equations. Besides, the results of this research indicated that using the EBRIG system through vertical grooves in RC beams with and without stirrups caused the energy absorption to increase about 85% and 97%, respectively, relative to the control.

• Steel and Composite Structures
• /
• v.42 no.6
• /
• pp.765-777
• /
• 2022

Ultra high performance concrete (UHPC) can be used in the UHPC-steel composite structures especially for bridge structures to achieve high stiffness and high fatigue resistance with low self-weight. The structural performances of UHPC-steel composite slabs subjected to hogging moment have a significant influence on the global stiffness and durability of UHPC-steel composite structures. In order to study the structural behaviors of non-steam-cured UHPC-steel composite slabs subjected to negative moment, five composite slabs combined the thin UHPC layers to steel plates via shear stud connecters with the diameter of 16mm were fabricated and tested under negative moment. The test program aimed to investigate the effect of stud spacing and longitudinal reinforcement ratios on the failure mode, load-deflection behaviors, cracking patterns, bond-slips, and carrying capacities of composite slabs subjected to negative moment. In addition, direct tensile tests for the dog-bone UHPC specimens with longitudinal reinforcement bars were carried out to study the effect of reinforcement bars on the tensile strength of UHPC in the thin structure members. Based on the experimental results, analytical models were also developed to predict the cracking load and ultimate load of UHPC-steel composite slabs subjected to negative moment.

• Journal of the Korean Wood Science and Technology
• /
• v.46 no.6
• /
• pp.748-755
• /
• 2018

Timber from fast-growing tree species is susceptible to by biodeterioration attack, particularly subterranean termites. Impregnation with methyl methacrylate (MMA) potentially increases wood resistance to subterranean termite attack. Four wood species, namely sengon (Falcataria moluccana), jabon (Anthocephalus cadamba), mangium (Acacia mangium), and pine (Pinus merkusii), were impregnated with MMA, and samples of untreated and imidacloprid-preserved wood were prepared for comparison purposes. Small stakes, sized 0.8 cm by 2 cm in cross section by 20 cm in the longitudinal direction, were inserted into the ground for 3 months, and the weight loss of each specimen was determined at the end of the test period. A factorial $4{\times}3$ completely randomized design was used for data analysis; the first factor was wood species, and the second factor was treatment. The results showed that MMA polymer loadings were 27.88%, 24.91%, 14.14%, and 17.81% for sengon, jabon, mangium, and pine, respectively, and amounts of imidacloprid retention were $7.56kg/m^3$, $5.98kg/m^3$, $5.34kg/m^3$, and $9.53kg/m^3$, respectively. According to an analysis of variance, wood species, treatment, and interaction of both factors significantly affected the weight loss of wood specimens. Mangium had the smallest weight loss, followed by pine, sengon, and jabon. MMA impregnation into the wood increased the resistance of wood samples to subterranean termite attack during in-ground testing, but the resistance level was lower than that of imidacloprid-preserved wood. Except for mangium wood, the MMA treatment did not significantly affect resistance.

• Journal of Korean Society of Steel Construction
• /
• v.24 no.1
• /
• pp.35-46
• /
• 2012

With the increase in the demand for high-rise buildings, the use of high-strength steel has likewise increased. Thus, it has become more necessary to study the resistance force of the high-strength hollow structural section (HSS) joint of 600MPa. Additionally, the current design equation in Korea limits maximum yield stress at 360MPa in the case of HSS. In other words, since the current specification does not apply to HSS of 600MPa, this study aims to investigate the applicability of design equations as well as examine the behavior of the connection through the experiment and finite element analysis (FEA) of the plate-tube connection of 600MPa. In particular, this paper presents the behavior of joints with the gusset plates welded in the longitudinal direction of the circular hollow section (CHS) when the joints are subjected to lateral force. Comparing design equations with the results of FEA and the test, existing design equations are underestimated to be 56~79% in the case of high-strength materials.

• Steel and Composite Structures
• /
• v.34 no.1
• /
• pp.17-34
• /
• 2020

This paper investigates the flexural behavior of concrete beams reinforced longitudinally with either steel bars, molded glass-fiber reinforced polymer (GFRP) grating mesh or pultruded glass-fiber reinforced polymer (GFRP) grating mesh, under four-point bending. The variables included in this study were the type of concrete (normal weight concrete, perlite concrete and vermiculite concrete), type of the longitudinal reinforcement (steel bars, molded and pultruded GFRP grating mesh) and the longitudinal reinforcement ratio (between 0.007 and 0.035). The influences of these variables on the load-midspan deflection curves, bending stiffness, energy absorption and failure modes were investigated. A total of fifteen beams with a cross-sectional dimension of 160 mm × 210 mm and an overall length of 2400 mm were cast and divided into three groups. The first group was constructed with normal weight concrete and served as a reference concrete. The second and third groups were constructed with perlite concrete and vermiculite concrete, respectively. An innovative type of stirrup was used as shear reinforcement for all beams. The results showed that the ultimate load of the beams reinforced with pultruded GFRP grating mesh ranged between 19% and 38% higher than the ultimate load of the beams reinforced with steel bars. The bending stiffness of all beams was influenced by the longitudinal reinforcement ratio rather than the type of concrete. Failure occurred within the pure bending region which means that the innovative stirrups showed a significant resistance to shear failure. Good agreement between the experimental and the analytical ultimate load was obtained.

• Geotechnical Engineering
• /
• v.11 no.2
• /
• pp.139-156
• /
• 1995

A set of field investigations was performed to estimate accurately the predominant periods of seismic 8round motions and the attenuation characteristics of the seismic ground vibration. Predominant periods of ground motions were estimated from the measurement of the continuous microseismic vibratins of certain periods, inherent in the ground and in the buildings, utilizing the high sensitivity digital velocity seismometer consisting of 3-component geophones and a digital seismograph. Estimated predominant periods of microseismic vibraion of the ground(measured on'the ground surface) and the building (measured on the second floor) were in the range of 0.18~0.235 sec. and 0.26~0.31 sec. respectively. The subsurface structure of the site ground was surveyed by the seismic refraction method utilizing the digital seismicwave probing system. The ground structure was found to be a two-layered system : an upper top soil layer of 7m in thickness with the P-wave velocity of 662m1sec and a lower layer of silty-clayey soils with the P -wave velocity of 2210m1 sec. The attenuation characteristics of the seismic ground vibrations were determined by the amplitude decay measurement method us;ng the Seisgun, which produces strong artificial seismic energy. Measured spatial attenuation coefficients of the ground vibration in vertical(Z) longitudinal(X), transverse(Y) direction were 0.1137, 0.0025, and 0.0290 respectively. Estimated Spartial QP's (inverse of the specific dissipation constant w.r.t. shear waved of X, Y, and Z directions were in the range of 5.913~7.575, 32.371~41.452, 2.794~3.579 re spectively. This indicates that aseimic design of the structures on the site should take stronger consideration regarding the earthquake resistance characteristics of the structures against longitudinal ground motion.

• International Journal of Highway Engineering
• /
• v.11 no.1
• /
• pp.203-215
• /
• 2009

This study was conducted to develop the design methodology of longitudinal post tensioning for the post-tensioned concrete pavement (PTCP). The longitudinal stress distribution in the PTCP slab was analyzed when post tensioning was applied. Then, the tensile stress distribution in the PTCP slab due to the environmental and vehicle loads needed for the design was investigated. In addition, prestress losses were calculated considering the losses due to the frictional resistance between the slab and underlying layer and due to various reasons related to tensioning. The tensile stresses used for the design were obtained by adding the stresses from the critical conditions under both the environmental and vehicle loads. The prestress losses were obtained by considering actual field conditions. The effective post tensioning amount was determined by considering the design loads including environmental and vehicle loads and various losses, and the effect of the allowable tensile stress on the post tensioning amount was investigated. The initial stage of the design of the longitudinal post tensioning is to obtain the stresses under the design loads and the required prestress determined by subtracting the allowable tensile stress from the design stress. Then, the optimal tendon spacing and the tensioning amount can be obtained by comparing with the effective tensioning amount including various stress losses.

• Korean Journal of Radiology
• /
• v.24 no.3
• /
• pp.235-246
• /
• 2023

Objective: It is difficult to predict the treatment response of tissue after stereotactic radiosurgery (SRS) because radiation necrosis (RN) and tumor recurrence can coexist. Our study aimed to predict tumor recurrence, including the recurrence site, after SRS of brain metastasis by performing a longitudinal tumor habitat analysis. Materials and Methods: Two consecutive multiparametric MRI examinations were performed for 83 adults (mean age, 59.0 years; range, 27-82 years; 44 male and 39 female) with 103 SRS-treated brain metastases. Tumor habitats based on contrast-enhanced T1- and T2-weighted images (structural habitats) and those based on the apparent diffusion coefficient (ADC) and cerebral blood volume (CBV) images (physiological habitats) were defined using k-means voxel-wise clustering. The reference standard was based on the pathology or Response Assessment in Neuro-Oncologycriteria for brain metastases (RANO-BM). The association between parameters of single-time or longitudinal tumor habitat and the time to recurrence and the site of recurrence were evaluated using the Cox proportional hazards regression analysis and Dice similarity coefficient, respectively. Results: The mean interval between the two MRI examinations was 99 days. The longitudinal analysis showed that an increase in the hypovascular cellular habitat (low ADC and low CBV) was associated with the risk of recurrence (hazard ratio [HR], 2.68; 95% confidence interval [CI], 1.46-4.91; P = 0.001). During the single-time analysis, a solid low-enhancing habitat (low T2 and low contrast-enhanced T1 signal) was associated with the risk of recurrence (HR, 1.54; 95% CI, 1.01-2.35; P = 0.045). A hypovascular cellular habitat was indicative of the future recurrence site (Dice similarity coefficient = 0.423). Conclusion: After SRS of brain metastases, an increased hypovascular cellular habitat observed using a longitudinal MRI analysis was associated with the risk of recurrence (i.e., treatment resistance) and was indicative of recurrence site. A tumor habitat analysis may help guide future treatments for patients with brain metastases.