EXPERIMENTAL STUDY OF REINFORCED CONCRETE DAPPED ENDS BEAMS STRENGTHEN WITH TRANSVERSE SUBSEQUENT INSTALLED BARS

This study involves in taking seven reinforced concrete dapped end beams strengthened with transverse Subsequent installed bars under concentered loads. These specimens of dimension (length=1220 x height=240 x width=130mm) with two types of sections (i.e. without and with transverse opening) and studied to evaluate the response of test beams to compare the strength capacity of beams strengthened with transvers subsequent installed bars relative to beams with or without opening region in sections. All specimens are simply supports. The five of R.C. dapped ends beams are strengthened with transverses Subsequent installed bars with or without opening and designed to test up to failure. Three parameters were investigated: compressive strength, amount of transvers Subsequent installed bars, and effect of section (with and without opening). It is found that’s increased in compressive strength by about 20% give increase in load carrying capacity by about 9%. Also, the reinforced concrete dapped ends beams contains transverse opening section compared to beams without opening results show decrease in strength capacity and gives more deflection by about in range (10-20%) and (18-26%) respectively. The transverse Subsequent installed bars are provided by steel bolts diameter of 10.5mm gives more enhancement in strength capacity and decrease deflection more than the others without transvers bars by about (8-77%) & (20-30%). Strengthened of beams by transvers bars can show to again in ultimate strength capacity by about (30%).


Introduction
Reinforced concrete (RC) beams with dapped ends are frequently found in bridge girders and precast concrete construction. The dapped-end beam provides an economical and efficient means of connecting precast to precast and precast to cast in place concrete members.
It enables reduction in the construction depth of a precast concrete floor or roof structure, by recessing the supporting corbels or ledge into the supported beams (Lu et al., 2003). Reinforced concrete dapped-end beams have many applications as drop-in beams between corbels or beam-to-beam connections (Yang et  Typically, reinforcement for a dapped-end beam with a /d ≤ 1 is composed of the main bars, hanger bars and horizontal stirrups. According to Wang and Hoogenboom (2005), inclined stirrups and longitudinal bent reinforcement have greater shear capacity than vertical stirrups for dapped-end beams with a /d < 1. Vertical stirrups, however, may play a significant role in the shear-carrying capacity of dapped-end beams with a/d > 1 (Mattock and Chan, 1979).

Objective of Study
The objective of the present research was to show the effect of strengthening provided by Subsequent installed bars. Variables included, concrete strength, opening region and transverse strengthen by post-tension bars arrangement and layout.
Also to get way to develop method of strengthen to get equivalents beams with opening strengthen with posttension transvers that give same load capacity of beam without opening sections.

Experimental program
This program consist of seven R.C. dapped ends beams was investigate to show the behavior of specimens when strengthened with transvers vertical Subsequent installed bars.
The experimental program described in this study incorporated seven beams with dapped ends; two without opening main defects were intentionally introduced compressive concrete strength as reference specimens, opening region (location and number of bars (bolts)) through cross section and five different strengthening techniques were applied.

Materials
In this study, the mixes of the concrete were consist of ordinary Portland cement, irregular gravel of (19 mm) maximum size, and sand.
The mix proportioning began with the selection of the unit weight (wet density) are given in Table 1 for all beams .
The mix was then proportioned by the method of absolute volumes of one cubic meter are obtained by series test of trial mixes. Table (1) shows final adopted mix of designs. The average compressive strength of concrete (standard cylinder (150 x 300mm)) fc` of these mixer of 28 days are 25 and 30 MPa.

Dapped End R.C. Beams Details
Seven reinforced concrete dapped end beams with details shown in Table (2) were designed, fabricated and tested up to failure. All beams are simple support, two without opening, three beams had a transvers recess of diameter (50 mm) in the bottom fiber and five beams had strengthen with transvers Subsequent installed bars with different number of subsequent installed bares as shown in Figs.(1,2 and 3).
The transvers vertical subsequent installed bars system used in this work to provide more strength capacity and strengthen the discontinuous edges of beams. Before casting specimens all components were thoroughly hand mixed for at least 3 min to get homogenous mixture.
After finish cast the concrete to the molds as shown in figures. When complete 28 days of curing the specimens ready to strengthen by transvers vertical bars. The properties of materials and strength are shown in Tables (2). *: According to ASTM A615/615M-08a **: Average of three specimens (Bars of length 500mm)

Instrumentation and Testing Procedure
The specimens are painted with white colures after complete of curing duration. Then the beams are moved to position under two points of concentrated load.
During the testing stage we will recorded the deflection at mid span and near support at each of load increment (every 5 kN), the deflection measured using digital dial gauge of capacity 3 cm and accuracy of 0.01) the instrument and layout of specimens are shown in Fig.(5). The test is continue till failure .
a. Testing Machine b. Test Setup.

First Crack and Ultimate Load
The comparison between different variables that will take in this study based on first crack, ultimate load and deflection are listed in Table (5 and 6).

Variables Effect and Ultimate Load
The comparison between specimens based on variables are shown in Fig.(6).These were the compressive strength, transvers subsequent installed bars, opening region and section types.

Crack Patterns
From tested all specimens that shows transverse subsequent installed bars has effect on crack propagation and numbers of crack.
The typical crack pattern and failure modes of tested beams reported in this paper are shown in Fig.(8).
In the tests, cracks always initiated at the reentrant corner of the tested beams at approximate 40o-60o to the axis of the beam, resulting in a redistribution of stresses causing increasing steel stresses, bond stresses and some bond slip [4].
Under an additional load these cracks spread, increased in number and reduced the compression zone of the beam considerably. At one or a few load increments before failure, more inclined cracks, occurred at the reentrant corner of the majority of dapped end beams, and steeper (50 o -70 o ) than the first inclined crack up to the vicinity of the load point.
In summary, the higher load carrying capacity led to appear more cracks, this gives larger difference in cracking loads due to conditions )) as shown in figures.

Load Deflection Behavior
The load deflection curves of all reinforced concrete dapped ends beams at the center of tension face (bottom fiber) are shown in Fig.(9). ((The load deflection at point near dapped end that's give same behavior of central point. These Figures, show the same behavior of load -deflection curve because the same properties and strength of materials that used in construction of beams. When used transvers subsequent bars due to same reason the deflection decreased by about (15-30%), (8-27%) respectively. The opening provide by transvers circle holes diameter of 50 mm that lies in tension fiber of beams has little effect on load carrying capacity or deflection by about 7 to 15%.