Normal Reinforced Concrete Research Articles

Blast Resistance of Polyethylene Fiber Reinforced Concrete to Contact Detonation

When designing blast-resistant reinforced concrete (RC) structures, reducing spall damage due to reflected tensile stress waves is a major problem. To investigate the applicability of polyethylene fiber reinforced concrete (PEFRC) for use in blast-resistant RC structures, experimental investigations were conducted to evaluate the damage to PEFRC slabs subjected to contact detonation. As a result, it was shown that PEFRC was effective in reducing the spall damage due to contact detonation as compared with normal RC. Moreover, an equation for estimating damage depth to the PEFRC slab subjected to contact detonation was derived based on the test results.

Finite Element Simulation of FRP Strengthened Reinforced Concrete Slabs under Two Independent Air Blasts

Multiple detonations might occur in both accidental explosions and terrorism attacks. Generally, normal reinforced concrete (RC) structures which are not designed to withstand high intensity blast loads are not capable of withstanding explosions from a single blast let alone a sequence of more than one blast. Since concrete is often highly cracked and damaged from the first blast, the remaining deteriorated concrete and steel reinforcement in a RC member becomes very vulnerable to collapse. This paper reports on the feasibility of using fibre reinforced polymer (FRP) to strengthen a normal RC slab capable of sustaining two independent air blasts. Apart from the experimental investigation, numerical studies have been conducted to verify the concrete and FRP material models when they are utilized to predict the behaviour of FRP-RC structures under multiple blasts. This article provides guidance on how to choose appropriately between the two existing concrete models available in the LS-DYNA code.

CFRP 시트 및 강섬유로 보강된 RC 보의 충격저항 성능 평가

최근 콘크리트 구조물에 충격하중, 폭발하중 등 극한의 외력이 작용하는 경우가 빈번하게 발생하고 있다. 이 연구에서는 강섬유보강 RC보와 carbon FRP 시트를 이용하여 보강한 RC보를 이용하여 충격실험을 진행하였다. 강섬유 보강 RC보의 경우 0.75%부피비로 강섬유를 혼입하였으며 carbon FRP 시트의 경우 에폭시 레진을 이용하여 보강을 한후 보 부재를 완성하였다. FRP 시트 보강은 부재의 하단을 휨 보강하였으며 충격하중이 부재에 작용할 때 발생하는 shear-plug 균열을 제어하기 위하여 충격하중이 가해지는 국부에 CFRP 전단보강을 실시하였다. 실험진행은 drop-weight test 방식으로 직접 기기를 만들어 실행하였다. 각각의 부재에 단계별로 충격하중을 가하여 실험을 진행하였으며 균열과 균열폭을 측정하였다. 실험결과 강섬유보강 RC보가 일반 RC보에 비하여 균열폭 및 shear-plug 균열제어 그리고 스폴링 파괴에 더 높은 성능을 나타내었다. FRP로 부재의 하단을 휨 보강한 부재의 경우 균열의 제어에 어느정도 효과를 나타내고 있으나 충격하중이 가해질 시 콘크리트와 FRP 시트의 부착면에서 박리파괴가 빠르게 진행되었다. FRP 시트로 부재의 하단과 측면을 CFRP로 휨, 전단보강한 부재의 경우 shear-plug 균열제어에 가장 높은 저항성능을 보이고 있음을 확인할 수 있었다. 하지만 충격하중이 보강이 이루어지지 않은 부분에 작용할 경우 오히려 보강이 되지 않은 RC보에 비하여 콘크리트 스폴링 파괴에 더 취약함을 알 수 있었다.

Blast testing of ultra-high performance fibre and FRP-retrofitted concrete slabs

A series of tests was conducted to investigate the blast resistances of slabs constructed with both plain ultra-high performance fibre concrete (UHPFC) and reinforced ultra-high performance fibre concrete (RUHPFC), and slabs reinforced with externally bonded (EB) fibre reinforced polymer (FRP) plates. Normal reinforced concrete (NRC) slabs were tested as control specimens. LVDTs and pressure transducers were used to record deflection histories, and pressure sensors located at the centre and one edge of the slabs measured airblast pressure histories. The measured pressures at the centre and edge of the slabs were significantly different from those estimated using traditional procedures such as those in TM5-1300. Tests indicated that the plain UHPFC slab had a similar blast resistance to the NRC slab and that the RUHPFC slab was superior to both. The addition of EB carbon FRP plates to the compression face of a reinforced concrete slab increased its ductility and blast resistance. Test results were compared with the maximum energy absorptions predicted from layered capacity analyses of the NRC, retrofitted, plain UHPFC, and RUHPFC specimens.

Flexural Fracture and Fatigue Behavior of RC Beams Strengthened with CFRP Laminates under Constant Amplitude Loading

Externally bonded carbon fiber reinforced polymer (CFRP) materials are well suited to the rehabilitation and reinforcement of civil engineering structures due to their high specific strength, specific stiffness and corrosion resistance. To probe the fatigue behavior of CFRP strengthened concrete structures, three point bending experiments of reinforced concrete (RC) beams strengthened with carbon fibre laminate (CFL) under constant amplitude loading were performed. The histories of midspan flexibility and bending stiffness of strengthened beams were recorded automatically. And the linear curve between fatigue strength and the logarithm of fatigue life was obtained. The failure modes go through concrete cracking, CFL debonding from concrete and steel bars yielding and fracture with increasing cycles of fatigue loading. Bonded CFL increases the ductility of strengthened RC beam and results in dense distribution of cracks compared with normal RC beam, and it’s bending stiffness at damage state as well. The fatigue damage evolvement shows three stages of nucleation, steady expansion and failure. Then the failure mechanism was studied and a cumulative damage model was proposed to describe the fatigue damage and fracture process of CFL strengthened RC beams under constant amplitude loading.

Design of Reinforced and Prestressed Concrete Inverted T Beams for Bridge Structures

P refabricated concrete stringers with cast-in-place slab are frequently used to achieve economical and speedy bridge construction schemes. Beams constructed in the form of an inverted T possess on each side of the web a bracket or flange overhang that provides a convenient shelf or supporting surface for the precast stringers. Hence, castin-place, post-tensioned, prestressed concrete (PC) and reinforced concrete (RC) inverted T beams are frequently used in bridges as bentcap girders as indicated in Fig. 1. Inverted T beams can he simply supported, cantilevered over simple supports, or they can be constructed monolithically with columns or piers. They reduce overall floor depth by avoiding deep cross members beneath prefabricated stringers, resulting in lower abutments and shorter approaches for the bridges. Despite its frequent use for at least the past two decades, the inverted T shape remains as one of the least investigated cross sections. At present, no guidance for handling design problems specifically associated with the inverted T section is available in current North American standards. Consequently, engineers have tended to rely on per,sonal judgment and discretion for design of inverted T girders. This paper summarizes design recommendations that are based on observations and analyses of cast-in-place normal weight, PC and RC laboratory test specimens reported in studies of inverted T beams °-' The paper is directed