Showing papers in "Journal of Structural and Construction Engineering (transactions of Aij) in 2003"

Experimental study on buckling-restrained braces using steel mortar planks

Abstract: The authors have conceived the buckling-restrained braces (BRBs) providing stable hysteretic behavior under the high-strain conditions. The compressive strength of BRBs generally tends to be higher than the tensile strength. The authors assumed that it was because of friction force between the surface of core plate and the restraining part, and that the magnitude of friction force was related to the buckling mode number resulting in the increase of contact points. A set of prediction formulas for the buckling mode number has been proposed in the authors' previous study. In this paper, the validity of the proposed formulas for the buckling mode number is examined by the test results of strain gauge measurement on the core plate from the cyclic axial-loading tests. Furthermore, the relationship between the strength ratio of the compressive to tensile strength and the slenderness ratio of plastic region of core plate is estimated. As a result, 1) the progress of the buckling mode shape is successfully observed from the test results, and 2) the proposed formulas correspond approximately to the upper and lower bounds of the buckling mode number and also estimate quite well the strength ratio from the test results.

An investigation on aspects of damage to precast concrete piles due to the 1995 hyougoken-nambu earthquake

Abstract: Aspects of typical damage at deeper underground part of precast concrete piles, referred to as the K-shaped (in Japanese character pronounced "ku") failure in this paper, have been investigated. Such failures are attributed to lateral flow at liquefied reclaimed land, such as Port Island and Rokko Island in Kobe city, during the 1995 Hyogoken-Nambu earthquak. A simple static analysis proposed earlier by the first author and referred to as the load distribution method has been utilized to evaluate the horizontal resistance of piles and to investigate the cause of this type of failure. Results of the analysis show that bending stresses in piles exceed pile strength. In addition, the shearing stress at slip surface formed by liquefied soil layer is close to the ultimate strength. It is shown that the effects of lateral flow on piles may be effectively represented by the combination of distributed load arising from active earth pressure due to separation of frontward soil from piles and the concentrated load corresponding to the slip force in soil behind the piles.

Measurement of wind-induced response of buildings using rtk-gps and integrity monitoring

Abstract: An RTK-GPS (Leica MC1000) has a nominal accuracy of ±1cm +1ppm for horizontal displacements with a sampling rate of 10Hz. The object of this paper is to demonstrate the feasibility of RTK-GPS for wind-induced response measurements and its efficiency in measuring the displacement of a full-scale tower and to study the feasibility of hybrid use of FEM analysis and RTK-GPS for detecting the integrity of structures during strong typhoons. The efficiency of RTK-GPS is demonstrated in the full-scale measurement of an actual steel tower. According to the feasibility study of RTK-GPS for measuring wind-induced responses of buildings, the responses with amplitudes larger than 2cm and natural frequencies lower than 2Hz can be detected by RTK-GPS. Hybrid use of RTK-GPS and FEM analysis for real time monitoring of the integrity of structures is proposed and its efficiency is demonstrated. INTRODUCTION Wind-induced response consists of a static component, i.e. a mean value, and a dynamic fluctuating component. The static component is difficult to measure with accelerometers, which have been generally used so far. Celebi (1998) proposed the use of RTK-GPS (Real-Time Kinematic Global Positioning System) for measurements of dynamic responses of buildings. An RTK-GPS (Leica MC1000) has a nominal accuracy of ±1cm +1ppm for horizontal displacements and ±2cm +2ppm for vertical displacements with a sampling rate of 10Hz (Tamura et al., 1999, 1) Professor 2) Research Associate 3) Senior Researcher 4) Associate Professor 5) Associate Professor 2000, 2001). Considering the static component and the first mode predominance for wind-induced responses, GPS is better for wind-induced response measurements. The objects of this paper are to study the feasibility of RTK-GPS for wind-induced response measurements and to demonstrate its efficiency in measuring the displacement of a full-scale tower. Then, hybrid use of RTK-GPS and FEM analysis for real time integrity monitoring of structures is proposed. PRINCIPLE OF RTK-GPS GPS surveys the distance from a certain point on the earth to a GPS satellite by measuring the exact traveling time of an electric wave transmitted from the satellite to an antenna at the measuring position. GPS generally requires 4 satellites to obtain the information of 3 components at a position (X,Y,Z) and the time. However, RTK-GPS requires one more satellite for real-time high-frequency (10Hz) measurements. There are many causes for errors, e.g. PDOP (position dilution of precision), clock and orbit errors of satellites, ionosphere and troposphere delays, multi-path and so on. However, if two antennas relatively close to each other in the global scale receive the same electric waves from the same satellites simultaneously, the error sources should be the same. Therefore, if the position of one of the two points, i.e. the reference point, is fixed and exactly known, the error of the GPS survey can be accurately detected at any moment. If the error information obtained at the reference point is immediately transmitted as a correction signal to the other point, i.e. moving measuring point, the error of the position survey of the measuring point can be minimized. This is the outline of the position survey by RTK-GPS. ACCURACY OF RTK-GPS Before full-scale measurement of an actual tower’s response, the basic characteristics of RTK-GPS were examined. The background noise of the RTK-GPS survey was first examined. The GPS antennae not only at the reference point but also at the measuring point were fixed on the roof of a rigid 3-story RC building. Figure 1 shows an example of the10-min mean of the stationary point. The 10-min mean value fluctuated ±5mm, which can be thought to be the background noise of the RTK-GPS monitoring. It should be noted that the background noise was influenced by PDOP, which depends on the geometrical arrangement of the satellites. The accuracy of RTK-GPS in measuring sinusoidal displacements was next examined, using an electronic exciter. Figure 2 shows the set-up of the sinusoidal vibration tests. A GPS antenna was mounted on the exciter, and a wire displacement transducer was set to accurately measure the displacement. Figure 3 compares the temporal variations of the displacements measured by RTK-GPS and the wire displacement transducer. When the vibration frequency was lower than 2Hz and the vibration amplitude was larger than 2cm, RTK-GPS results seemed to closely follow the actual displacement.

Effect of uplift on earthquake response of building

Abstract: There was a light damaged office building, which was designed before establishing the new seismic design code, in seismic intensity VII area at the 1995 Hyogo-Ken Nanbu earthquake. According to our study, it seemed that uplift of base reduced the structural damage. So, it is important to understand an effect of uplift on earthquake response. In this paper, the effect of uplift on earthquake response of building was studied by nonlinear earthquake response analysis considering several types of structural characteristics. A simple formula for the condition of uplift was also studied. Analytical models consisted of one span and eleven stories frame and the frame with shear wall. As a result of nonlinear earthquake response analysis considering uplift, the frame with wall tended to cause uplift more than pure frame. Maximum shear force of the frame with wall was about half compare to that of the pure frame. Effects of structural characteristics (distance between supports, support stiffness, building stiffness) were also examined. The uplift occurred easily in case of narrow support and decreased to half base shearing force. The base shearing force varied according to stiffness of support and natural period of structure. Studies were also performed on the condition of uplift of structure through numerical analyses, in which aspect ratio, building stiffness and support stiffness were selected as main parameters using multi-mass model. Based on the analytical results, a simple formula for the condition of uplift was derived as a function of acceleration response spectrum value. It was found that the formula agreed well to the analytical results.