Masuhiro Beppu

Contact Explosion Resistance of Concrete Plates Externally Strengthened with FRP Laminates

The present work is intended to evaluate the effectiveness of fiber sheet reinforcement on explosive-resistant performance of concrete plates. Carbon fiber sheets or aramid fiber sheets have been employed to reinforce concrete plates. Explosion tests have been conducted to examine the effect of fiber sheet reinforcement on local damage and fragmentation of concrete plates. Test data are compared with the estimated values formulated by Morishita et al. and the characteristics of local damage are discussed. Local damage of concrete plates reinforced by carbon or aramid fiber sheets has been extremely reduced as compared with that of concrete plates without fiber sheet reinforcement. These fiber sheets also have prevented concrete plates from fragmentation.

Collapse Mechanisms of Seawall due to the March 2011 Japan Tsunami using the MPS method

On March 11 2011 a huge tsunami was caused by a magnitude 9.0 earthquake, which devastated the sea defenses in the Tohoku coastal region of Japan. We investigated one of the disaster areas, the Taro district, which had been very famous for having a 10m high seawall. This paper focuses on why the seawall in the Taro district collapsed during the tsunami. To this end the present work involves (1) the field disaster investigation, (2) the scale of the March 11 tsunami by performing its runup calculation, (3) the overflowing effects of the tsunami on the seawall by using the MPS (Moving Particle Semi-implicit) method, (4) the overflowing model test of a seawall and (5) the possible collapse mechanisms of the seawalls, in which they were mainly destroyed by the overflowing and the ensuing draw down wave of the tsunami.

Design Concept for Local Damage of Concrete Plates Subjected to High Velocity Impact

Local damage of concrete structures, i.e. spalling, scabbing and perforation, would occur when concrete structures are impacted by high velocity projectiles. To propose protective design of concrete structures against high velocity impact, failure mechanism of local damage of concrete plates should be investigated. The authors have studied on failure mechanism of the local damage through impact tests and numerical analyses. This study presents a design concept for the local damage of a concrete plate subjected to high velocity impact. In the design procedure, occurrence of scabbing is judged based on comparison between maximum impact load and scabbing resistant capacity of the concrete plate. Impact load history and penetration depth are calculated using the modified theoretical model, and scabbing resistant capacity is estimated by applying a modified formula for punching shear resistant capacity.

A fundamental investigation of reinforced concrete beams subjected to close-in explosion

This study investigates a reinforced concrete beam subjected to a close-in explosion. In a series of tests, the scaled distance was varied from 0.045 m/kg1/3 (contact) to 0.30 m/kg1/3. The measurement parameters were failure state, pressure distribution, residual displacement at the center of the beam, and reaction force. The experimental results showed that the pressure waveform closer to the center of the reinforced concrete beam had considerable peak pressure and a sharp rise-time. Moreover, the loading duration at the ends of the beam was increased as compared to that at the center. The intensity of the local failure region and the residual displacement at the center of the beam increased with decrease in the scaled distance. Referring to previous studies on failure prediction of a reinforced concrete slab and beams subjected to close-in explosion, their prediction methods for local failure were compared to test results. Numerical simulations were performed to investigate failure characteristics of the reinforced concrete beam. The numerical results demonstrated that the peak pressure and impulse in the central part were considerably high as the scaled distance decreased. The numerical simulations effectively reproduced failure characteristics of the reinforced concrete beam.

A method for evaluating the local failure of ultra-high-performance short polyvinyl alcohol fiber-reinforced concrete panels subjected to a projectile impact

This study investigated local failure characteristics and failure limit thicknesses of an ultra-high-performance fiber-reinforced concrete panel reinforced with polyvinyl alcohol by conducting impact tests. In a series of tests, steel hemispherical projectiles with a mass of 46 g collided with ultra-high-performance fiber-reinforced concrete panels reinforced with polyvinyl alcohol. The ultra-high-performance fiber-reinforced concrete panels reinforced with polyvinyl alcohol with thicknesses in the range of 30–90 mm were tested at the impact velocities of 170–500 m/s. The experimental results revealed that the penetration depth or scabbing damage induced by the impact was significantly suppressed for the ultra-high-performance fiber-reinforced concrete panel reinforced with polyvinyl alcohol compared to that of a plain concrete panel. The experimental results demonstrated that local failure intensity for the panels was similar at equivalent impact energies, regardless of the combination of projectile mass and impact velocity. Based on the test results, we proposed a method for evaluating the penetration depth and scabbing limit thicknesses by the impact energy.

A Study on Structural Behavior of Reinforced Concrete Walls Exposed to Hydrocarbon Fire Under Vertical Load

In order to investigate the structural behavior of a reinforced concrete wall exposed to a hydrocarbon fire while under a vertical load, fire-resistance tests and numerical analyses are carried out on small-scale reinforced concrete wall specimens. During the fire tests, the wall specimens deform toward the heated side during the early stages of fire. Later they deform toward the non-heated side and finally fail through bending and compression. In numerical analyses to simulate the structural behavior of the small-scale wall specimens, transient creep strain of concrete is calculated assuming dependence on concrete temperature and rate of temperature rise. The results of numerical analyses are in relatively good agreement with the experimental results with respect to vertical deformation of the wall when the amount of transient creep strain is reduced when the rate of concrete temperature rise exceeds 7.5–10.0 K/min.

Proposal on risk assessment of reinforced concrete structures subjected to explosive loads

This study proposes an evaluation method to assess the risk of a reinforced concrete structure subjected to an explosive load such as that resulting from a terrorist bombing attack. First, a hazard curve that represents the relationship between the frequency of explosive incidents and the explosive mass was evaluated based on the statistics of terrorist bombing incidents. Second, to evaluate the damage state of the reinforced concrete structure due to the explosive load, fragility curves for the reinforced concrete members, such as beams, columns, and slabs, were evaluated using a single-degree-of-freedom model and a rotational capacity–based criterion. The fragility curve shows the relationship between the damage probability level, such as “no damage,” “small damage,” “collapse,” and an explosive mass. The total failure probability of the reinforced concrete structure was estimated by superposing the fragility curves of the members and by incorporating the reducing effect of floor slabs in the reinforced concrete structure on the blast load. A loss curve was drawn based on the damage state of the reinforced concrete structure by assuming the number of human lives lost and the reinforced concrete structure in each damage state. A risk curve was then derived by combining the hazard curve with the loss curve.

Failure behavior of reinforced concrete slabs subjected to moderate-velocity impact by a steel projectile

This study investigates the failure characteristics of reinforced concrete slabs subjected to moderate-velocity impacts by conducting impact tests and numerical simulations. In a series of tests, a spherical steel projectile with a mass of 8.3 kg and a diameter of 80 mm is collided with an reinforced concrete slab at an impact velocity of 65–90 m/s. To investigate the failure characteristics of the reinforced concrete slab, impact motion of the projectile, reaction force, and strain–time history on the back surface and reinforcing bars of the reinforced concrete slab were measured. Failure modes obtained experimentally were compared with the Central Research Institute of Electric Power Industry formula proposed for the local damage of reinforced concrete slabs. Test results revealed that a circular scabbing crack on the back surface of the reinforced concrete slab was completed while there is a sharp increase in the reaction force. Numerical simulations using a high-fidelity concrete model reasonably reproduced the failure characteristics of an reinforced concrete slab. Numerical results demonstrated that the scabbing failure of an reinforced concrete slab subjected to a moderate-velocity impact was initiated by the penetration of the projectile and was completed during the reaction force response.

Failure Behavior and Numerical Simulation of the Local Damage of Ultra High Strength Fiber Reinforced Concrete Subjected to High Velocity Impact

This study presents the local damage of ultra high strength fiber reinforced concrete plates. Impact test of the reinforced concrete plates using two different short fibers are conducted to examine the failure behavior and impact resistant performance. Material models are discussed and proposed by simulating the high speed tri-compressive and uni-tensile tests. Numerical simulations of the impact tests are carried out. Numerical results show good agreements with the test results.

Aramid Fiber Sheet Reinforcing Effects on the Local Damage in Concrete Plates Subjected to High Velocity Impact

This study intended to evaluate the effectiveness of fiber sheet reinforcement on local damage mitigation in concrete plates subjected to high velocity impact. High velocity impact tests were conducted using concrete plates externally reinforced with aramid fiber sheets to examine the effects of the number of the fiber sheet laminates on the local damage. In a series of impact tests, strain time histories of the fiber sheet laminates were measured. Numerical simulations using the hydrocode ANSYS AUTODYN were carried out to reproduce the reinforcing effects by the fiber sheet laminates. Numerical results are discussed by comparing strain behavior and failure simulated numerically with test results. The reinforcing mechanism by the fiber sheets is discussed based on the numerical results.