Kappyo Hong

Lateral buckling of I-section composite beams

Lateral buckling of a laminated composite beam with I-section is studied. A general analytical model applicable to the lateral buckling of an I-section composite beam subjected to various types of loadings is developed. This model is based on the classical lamination theory, and accounts for the material coupling for arbitrary laminate stacking sequence configuration and various boundary conditions. The effects of the location of applied loading on the buckling capacity are also included in the analysis. A displacement-based one-dimensional finite element model is developed to predict critical loads and corresponding buckling modes for a thin-walled composite beam with arbitrary boundary conditions. Numerical results are obtained for thin-walled composites under central point load, uniformly-distributed load, and pure bending with angle-ply laminates. The effects of fiber orientation, location of applied load, and types of loads on the critical buckling loads are parametrically studied.

Moment-rotation behavior of double angle connections subjected to shear load

Abstract Double angle connections, which are welded to the beam web and bolted to the column flange, are studied to establish the effect of bolt gage distance and angle thickness. An analysis is performed to establish the moment–rotation relationship for the double angle connections and the stress distribution of each specimen is observed. They are subjected to shear loads and the elastic–perfectly plastic constitutive law is assumed. The software package ABAQUS is used to analyze the nonlinear behavior of a double angle connection. To verify the finite element model analysis, experimental tests with the same geometric and material conditions as the analysis are also conducted.

Parametric study of double angle framing connections subjected to shear and tension

Abstract Double-angle connections, which are welded to the beam web and bolted to the column flange, are studied to establish the effects of the bolt gage distances and the angle thicknesses. Six steel angles are considered. For an angle section having three different thicknesses, two different bolt gage distances are analyzed. They are subjected to axial tensile loads, shear loads, and a combination of these loads. An elastic–perfectly plastic constitutive law is assumed. The software package ABAQUS is used to generate a double-angle framing connection. This three-dimensionsl (3D) finite element model consists of an angle, four bolts, springs, and half the beam web. In the development of the 3D finite element model, the contact problem between the angles and the bolt heads is considered in addition to the separation of the angle from the column. The load–displacement relationship and moment–rotation relationship of each connection with given loading conditions are established, as well as stress distributions for the angles. Experimental tests are conducted with axial tensile loadings for verification of the finite element model analysis.

A Practical Data Recovery Technique for Long-Term Strain Monitoring of Mega Columns during Construction

A practical data recovery method is proposed for the strain data lost during the safety monitoring of mega columns. The analytical relations among the measured strains are derived to recover the data lost due to unexpected errors in long-term measurement during construction. The proposed technique is applied to recovery of axial strain data of a mega column in an irregular building structure during construction. The axial strain monitoring using the wireless strain sensing system was carried out for one year and five months between 23 July 2010 and 22 February 2012. During the long-term strain sensing, three different types of measurement errors occurred. Using the recovery technique, the strain data that could not be measured at different intervals in the measurement were successfully recovered. It is confirmed that the problems that may occur during long-term wireless strain sensing of mega columns during construction could be resolved through the proposed recovery method.

A Strain-Based Load Identification Model for Beams in Building Structures

A strain-based load identification model for beam structures subjected to multiple loads is presented. The number of sensors for the load identification model is the same as the number of load conditions acting on a beam structure. In the model, the contribution of each load to the strains measured by strain sensors is defined. In this paper, the longitudinal strains measured from multiplexed fiber Bragg grating (FBG) strain sensors are used in the load identification. To avoid the dependency on the selection of locations for FBG sensors installed on a beam structure, the measured strain is expressed by a general form of a strain sensing model defined by superimposing the distribution shapes for strains from multiple loads. Numerical simulation is conducted to verify the model. Then, the load identification model is applied to monitoring of applied loads on a 4 m-long steel beam subjected to two concentrated loads. In the experiment, seven FBG sensors and nine electrical strain gages (ESGs) were installed on the surface of the bottom flange. The experimental results indicate a good agreement between estimated loadings from the model and the loads applied by a hydraulic jack.

Fire Resistance of the Korean Asymmetric Slim Floor Beam Depending on Load Ratio

Abstract In Korea recently, interest is increasing in slim floor systems that have superior structural performance and fire resistance. This paper contains the results of tests to confirm the fire resistance behavior of the composite asymmetric slim floor beam. The fire resistance behavior was analyzed using the finite element program ANSYS and the finite element models were validated against the test results. The validated thermal and structural models were used to predict the fire resistance of the Korean asymmetric floor beam and the average temperature of the steel bottom flange depending on load ratio changes. As a result, the 346ASB and the 350ASB were found to have 60 minutes of fire resistance when their load ratios were under 0.47 and 0.48 respectively without additional fire protection. Also, the authors have set the average temperature of the bottom flange, which has a direct impact on the ASB system, as a limiting temperature that enables gauging of its fire resistance as a table according to the load ratio, and presented the limiting temperature as a regression equation according to the fire resistance time.

Color and Material Property Changes in Concrete Exposed to High Temperatures

Abstract When a concrete structure is exposed to heat such as a fire, its material properties, such as weight, compressive strength and elasticity, are degraded. The exposure also accompanies cracking, spalling and color changes. Therefore, a structures quantitative damage assessment is very critical in determining whether to dismantle or strengthen the structure after a fire. The purpose of this study is to consider the color change of heat exposed concrete as a major parameter in conjunction with material property changes, such as weight loss and compressive strength degradation, for the purpose of identifying the relationship between concrete color change and material property changes at high exposure temperatures. For this purpose we manufactured concrete samples with varying water-to-cement ratios and heated them to target temperatures of 100, 200, 300, 400, 500, 600, 700 and 800°C in an electric oven, whereupon their color changes, weight losses and residual compressive strengths were measured for analysis. Experiment results show that the color change into red in concrete samples exposed to higher temperatures has a consistent relationship with weight loss rate and residual compressive strength. This result indicates that measuring the hue value in a concrete material can enable assessment of its material property changes.

Design of PC beam-column joint applied X-braced bars in the segmented structural system

AbstractThis study suggests a joint design using an X-brace bar to identify the stability and structural performance of a precast concrete (PC) beam-column joint design, which may cause problems when used in a segmented PC beam system for a long-span structure. For this, an experimental PC beam-column model at half scale was designed and verified for applicability of X-braced bars in a panel zone. While previous studies suggested the development of a longspan structural system using precast concrete (PC) and described the problems with PC beam-column joints, this study proposes a solution to improve the structural stability and performance of a PC beam-column joint design and conducts analytical verification.

PC Floor Systems for Microelectronics Manufacturing Buildings

Because a PC(Precast Concrete) system has to follow the transportation rules for transporting PC units and be designed to the specifications of the tools and equipment on site, designing long-span PC systems for microelectronics manufacturing facilities can be troublesome due to complications in transporting, lifting and handling the PC units. To resolve these problems that can occur in long span and heavy weight PC designs, this study proposes two types of long-span PC floor systems that practically use the traditional Gerber beam concept. In the proposed systems, long-span (17.4m) girders or beams are segmented into appropriate lengths using the Gerber system for easy delivery and lifting. Moreover, these systems provide the ability to optimally design massive units by controlling the location of hinge points. On the other hand, because continuous long-span girders or beams are segmented into the Gerber systems hinge points, these systems may generate structural stability problems during construction. Consequently, this study experimentally examines the structural performance of stress transfer mechanism in panel zones and the construction stability of PC units for columns and girders during assembly.

Estimation of Dynamic Load and Structural Vibration on Steel Plate Using Transfer Function

Abstract In general, vibration problems affecting the strength of members and serviceability of building structures are not considered in a structural design process. However, prediction of vibration is very critical and essential for structural designs, in particular, of structures that accommodate precision devices and products such as wafers and electronic microscopes. To predict the structural vibration of a floor, it is necessary to know various dynamic loads and dynamic characteristics of the floor. This study aims to predict the dynamic loads and structural vibrations of the steel plate in terms of the transfer function method. In order to know the dynamic loads and structural vibrations, a modal test and an impact excitation experiment were conducted multiple times on a steel plate. Results from the experiment were analyzed and compared against the measured excitation forces and vibration results. The results suggest that predicting the dynamic loads and vibration levels using the transfer function method is possible.