Norimitsu Kishi

Impact behavior of shear-failure-type RC beams without shear rebar

In this study, to establish a rational impact-resistant design procedure of shear-failure-type reinforced concrete (RC) beams, falling-weight impact tests were conducted. Twenty-seven simply supported rectangular RC beams without shear rebar were used. All RC beams were of 150 mm width and 250 mm depth in cross section, with rebar and shear-span ratios taken as variables. An impact load was applied at the mid-span of the RC beam by dropping a free-falling 300 kg steel weight. In these experiments, the impact force excited in the steel weight, the reaction force, and the mid-span displacement were measured and recorded by wide-band analog data recorders. After testing, crack patterns developed on the side-surfaces of the RC beams were sketched. The results obtained are as follows: (1) the shape of the hysteretic loop between the reaction force and the mid-span displacement can be assumed to be triangular when the RC beam collapses due to severe diagonal cracks developed from the loading point to the support points; (2) shear-failure-type RC beams without shear rebar under impact load can be designed with a certain safety margin by assuming a dynamic response ratio of 1.5 and an absorbed input energy ratio of 0.6; (3) the required static shear capacity for RC beams against impact load can be evaluated by a proposed simple equation.

A new nonlinear connection classification system

In this paper, a new classification system for steel beam-to-column connections in an unbraced frame is devised demarcating the moment–rotation diagram into three connection zones by two smooth nonlinear lines. The equations of these two nonlinear lines are taken from a three-parameter moment–rotation model. The three parameters used in the model are: initial connection stiffness Rki; ultimate moment capacity Mu of connection; and a shape parameter n. It was observed that the proposed classification system is simpler and more accurate than the existing classification systems.

Effective length factor of columns in flexibly jointed and braced frames

Abstract In order to rationally evaluate the stability of columns in flexibly jointed and braced frames, the governing equations for determining the effective length factor ( K -factor) of columns are derived considering the effects of the non-linear moment–rotation characteristics of beam-to-column connections. In this study, to derive the equations, the alignment chart approach is used and a recent study on the stability of flexibly jointed frames and the concept of the Shanleys inelastic column buckling theory are applied. With a proper evaluation of the tangent connection stiffness for semi-rigid beam-to-column connections at buckling state and with the introduction of the modified relative stiffness factors, the alignment chart in the present AISC-LRFD specification can be used to find the corresponding column K -factor in flexibly jointed frames. This is described in this paper. Furthermore, using two flexibly jointed and braced portal and one-bay two-story frame examples, the effects of the non-linear moment–rotation characteristics of connections on the K -factor are numerically studied and the K -factors obtained by two simplified methods are compared with the present method.

Dynamic Response Analysis for a Large-scale RC Girder Under a Falling-weight Impact Loading

In order to establish a rational impact resistant design procedure for prototype reinforced concrete (RC) structures, not only experimental study but also numerical analysis study should be conducted. However, numerical analysis method on impact response analysis for those structures has not been established yet. Here, in order to establish a rational numerical analysis method for prototype RC structures under impact loading, a falling-weight impact test was conducted for prototype RC girder with 8 m clear span. Referring to the experimental response waves, numerical accuracy was investigated varying major parameters. From this study, following results were obtained as: (1) fine mesh should be used near supporting gigues; (2) Drucker-Prager yield criterion should be applied which gives better results than von Mises one; and (3) appropriate system damping constant should be set to h = 0.015.

Elasto-plastic dynamic response analysis of prototype RC girder under falling-weight impact loading considering mesh size effect

This paper focuses on an applicability of the proposed numerical analysis method to the large scale RC girder under falling-weight impact loading using effective finite element mesh size distribution by comparing with experimental results. The results obtained from this study are: (1) displacement wave can be accurately estimated with seven-division of stirrup interval. (2) The maximum impact force and reaction force can be roughly estimated by using the mesh geometry with one-division for the each interval. (3) Damping constant should be used as 1.5%. (4) Drucker-Prager yield criterion should be applied. (5) The crack patterns can be roughly estimated with seven divisions between intervals of stirrup.

Behavior of tall buildings with mixed use of rigid and semi-rigid connections

Abstract Semi-rigid connections are rarely used in tall building frames. In this paper, the mixed use of rigid connections with semi-rigid connections for tall building frames as a way to reduce costs is investigated. Using the three-parameter power model for semi-rigid connections, a four-bay eight-story frame is numerically analyzed with four combinations of mixed use of rigid and semi-rigid connections. It is shown that normalized building drift Δ H can be kept under 1 400 by properly selecting the combination of rigid and semi-rigid connections.

Study of Eurocode 3 steel connection classification

The work provides an analytical evaluation of the Eurocode 3 classification on the three types of beam-to-column connections in steel construction. Extensive studies of the behavior of such connections in frames have been made, using the database compiled by Kishi and Chen. These studies showed that most connections have semi-rigid behavior for drift check at service load, but become flexible for strength check at factored load. The EC3 code provides a suitable classification for ultimate strength check but is not adequate for drift check.

Impact Response Analysis of Prototype RC Girders with Sand Cushion Using Equivalent Fracture Energy Concept

In order to establish a proper finite element model of prototype RC girder with sand element for impact response analysis, dynamic response analysis of RC girders with sand cushion subjected to impact force due to falling weight was performed to improve the state of the art of protective design for real scale rock-sheds using LS-DYNA code. Here, in order to establish a modification method for material properties of concrete so as to rationally analyze the prototype RC girder with sand cushion using coarse mesh, an equivalent fracture energy concept for concrete elements was proposed and the applicability was investigated comparing numerical analysis results with experimental results. From this study, it is confirmed that even though coarse mesh was used for prototype RC girder with sand cushion, similar results with those obtained using fine mesh can be assured.

Numerical Simulation of Reinforced Concrete Beams under Consecutive Impact Loading

In mountainous regions, galleries can be constructed over highways to provide protection from avalanches and falling rocks. Designing these structures requires the establishment of verification methods for serviceability and ultimate limit states. In this study, a three-dimensional elasto-plastic finite element analysis method using simple constitutive models is proposed to predict the accumulated damage and residual load carrying capacity of reinforced concrete beams under consecutive impact loading. This method is compared with experimental results to confirm its applicability. The results show that maximum deflection, residual deflection, and vibration characteristics after impact can be accurately predicted. The accumulated damage and residual load-carrying capacity can be predicted using the numerically analyzed vibration characteristics and maximum and residual deflections.

Numerical study for impact resistant design of full scale arch type reinforced concrete structures under falling weight impact test

In this paper, a falling-weight impact test using full scale arch type reinforced concrete (RC) structures was conducted to verify a proposed impact response analysis method. The applicability of the numerical analysis method was confirmed by comparison with the experimental results. The validity of the current impact resistant design procedure to the performance based design procedure was investigated using the proposed numerical analysis method. From this study, it is confirmed that by applying the current impact resistant design procedure, a performance based impact resistant design with a sufficient safety margin may be obtained for the full scale arch type RC structures.