Non-strengthened Specimens Research Articles

Characteristics of the deflection behaviour of a slab reinforced by an externally bonded fibre-reinforced polymer

In this study, the deflection test was conducted on a non-strengthened specimen and six reinforced concrete slabs reinforced with a fibre-reinforced polymer adhesion, and the behavioural characteristics owing to the differences in the material properties were determined. The experimental variables were the reinforcing materials, the pre-loading and the level of reinforcement. After the test, the effective moment of inertia suggested by ACI-318 and the moment of inertia computed from the experimental results were compared. As the level of reinforcement increased, the strength of slab also increased. From the analysis of the application of pre-loading, the pre-loaded slab exhibited a higher yield load and ultimate load than the non-pre-loaded slab. It was found that the effective moment of inertia suggested by ACI-318 underestimates the moment of inertia of the slab reinforced with the fibre-reinforced polymer.

Innovative method for strengthening dapped-end beams using an external prestressing technique

Dapped-end beams are precast members of concrete structures that are widely used in buildings and bridges. At the end of dapped-end beams, the discontinuities caused by the abrupt changes in cross-sectional dimensions, as well as the concentrated applied load, characterize this as a disturbed region. Improper dimensioning and distribution of reinforcing steel lead to undesirable cracking and failure mechanisms that must be predicted to apply proper strengthening systems. This article presents an experimental program for eight reinforced concrete beams with dapped ends. Seven specimens were strengthened using different shapes of external prestressing technique directions: horizontal, vertical and inclined. A non-strengthened specimen was investigated as a reference beam. The test results showed that vertical external prestressing techniques are a very effective strengthening method to increase the capacity of dapped-end beams up to 82 % compared to the control specimen. A new failure mode according to the strengthening technique using horizontal external prestressing appeared and led to compression failure. Additionally, a comparative study was conducted to evaluate the efficiency of various strengthening techniques. A strut-and-tie model was utilized in the analysis of such discontinuity in the D-region. A comparison between the present strengthening techniques and other previous work was conducted to provide a reasonable estimation of the efficiency of the results.

Seismic Collapse Prevention of Non-Structural Infill Masonry Using eq-top: an Easy Earthquake Fibre Retrofitting System

Specially manufactured technical textile and polyurethane glue, called “eq-top system” is proposed to save life and prevent collapse of non-structural masonry, e.g. in filled walls during a seismic event with a minimum cost. The idea is to attach glass fiber textile on the brittle brick partition walls in the buildings and connect them with the peripheral structural frames. During an earthquake it is expected that the system will hold the non-structural elements in place and prevent their out of plan failures; also it will improve their in-plane stiffness making them working as structural infill walls. The proposed technical textile is light-weight, easy to handle, fast in application, and cheap compared to the well-known FRP and CRP. To test the eq-top system, shake table on full scale brick wall specimens was conducted at Bogazici University in Turkey. The strengthened specimen and the non-strengthened specimens were fixed on the same shake table for a direct comparison and the amplitudes of base accelerations were increased until severe damage is reached in the non-strengthened and/or strengthened specimen. The seismic performance of the 2 × 2 specimens (two without and two with strengthening) was compared in terms of stiffness, strength, deformability and ductility. All thought that the specimens were excited under their resonance frequencies, no damage at all occurred in the strengthened specimen and total collapse happened already in the non-strengthened panel under low amplitudes. The results have confirmed effectiveness of the proposed retrofit scheme.

The seismic improvement and control of weak concrete frames with partial concrete shear walls

Controlling the lateral movement of buildings under earthquake effects is very important to prevent total collapse and therefore reinforced concrete (RC) shear walls are used to obtain the lateral stability of such buildings. In this study, the usability of partial RC shear walls to strengthen buildings with weak earthquake behavior was investigated. The basic parameters of the study were determined to be the ratio of shear wall height to shear wall length (Hw/Lw ) and whether the upper inflection point of the bent bar, a steel bar commonly used in the beams of RC buildings in Turkey, is integrated into or bent outside of the partial shear wall section. Three units of two-story, double-span weak RC frames were produced at a one-third scale. Two of these three frames were then strengthened by partial shear walls integrated on both sides of the central column. Strengthened and non-strengthened specimens were tested under reversed-cyclic lateral loading. The frame systems strengthened via partial RC shear walls showed significant improvement in strength and stiffness. No debonding was observed in the anchorage rods used in the shear wall-foundation connection.

고장력 인장봉으로 보강된 RC 보의 휨 거동에 관한 실험적 연구(3)

Unlike external bonded steel plate or carbon fiber, the external unbonded strengthening using hi-strength bar has some advantages in speed and simplicity of installation. It is not required surface preparations and not affected by environmental conditions. A set of nine laboratory tests on RC beams strengthened using the hi-tension bars are reported. Anchoring pin developed in former research is installed at the end of beam to connect the hish-tension bar to RC beam. The test results strengthened by hi-tension bars are compared with those of non-strengthened specimens. The main test parameters are the cross-sectional area of the high-tension bar, distance of stirrups and condition of supports. Test results show that the beams reinforced are superior to reference specimens, especially for the strength and deformation capacity. Also, shear resisting effect of hi-strength bar can be confirmed in the specimens which have lack of stirrups.

FRP SEISMIC RETROFIT OF RC SQUARE HOLLOW SECTION BRIDGE PIERS

The research work presented in this paper deals with the seismic assessment of hol-low bridge piers strengthened with fibre-reinforced polymer (FRP). The scope of the strengthening is to overcome some common deficiencies derived from the use of non-seismic design rules, which can often lead to inadequate response when operating in cyclic loading. The strengthening design was studied by means of a parametric analysis considering different fibres and geometrical parameters applied to typical case studies. Quasi-static cyclic tests were performed on five 1:4 scaled piers designed according to old non-seismic Italian codes and strengthened according to the previous analytical study. Efficiency of FRP strengthening was evaluated by comparing the experimental results with those obtained in a previous experimental research performed on similar non-strengthened specimens. Base shear versus lateral deflection curves, dissipated en-ergy and collapse mechanisms comparison shows the achievable effectiveness once the debonding risk has been overcome.