EFFECT OF BIG SERVICE HOLES ON STRENGTH CHARACTERISTICS OF REINFORCED CONCRETE SLENDER BEAMS

Abstract

Reinforced concrete slender beams are the most common beams encountered on daily basis in the Nigerian construction industry. There is always the need to introduce service holes into these beams for the purposes of service pipes. Researches into the behavior of deep beams with holes are extensively carried out. However, research into the behavior of slender beams with big service holes is rare and attracts little attention. Hence, the focus of this research work is to investigate the effect of big service holes on the strength characteristics of reinforced concrete slender beam. A total number of ten beams cast using 20.8 N/mm² concrete strength. The cross-sectional dimensions of the beams are 100mm x 150mm, a span of 1000mm and a effective length of 750mm. The tested beams consisted of two control beams without holes. The experimental beams consisted of eight beams, each of the four beams are with 50mm and 40mm service holes respectively (two of the beams have holes at the center, while the remaining two beams have holes at the supports). The reinforced concrete beams { 2Y 12}, are cured by immersion in water in a curing tank and tested at 28th days. The beams service holes are placed in two different locations: the first location of the service holes is at the supports and the second location is at the center of the beam, these being the positions of maximum shear force and maximum bending moment respectively. The control beams and experimental beams are subjected to point loads. The estimated ultimate load for the control beam loaded at centre (E0) is 70.13 kN, while the estimated shear capacity is 56.83 kN. The average actual ultimate load for the experimental beams with 50mm holes at supports and center (A01, AO2, B01, and B02) were 42.85 kN and 62.26 kN respectively, the average actual ultimate load for experimental beams with 40mm holes at supports and center (C01, CO2, D01, and D02) were 49.48 kN and 63.28 kN respectively, while the average actual load for the control beams (E01 and E02) was 63.80 kN. The average actual ultimate shear capacity for the experimental beams with 50mm holes at supports and center (A01, AO2, B01, and B02) were 21.43 kN and 31.13 kN respectively, the average actual ultimate shear capacity for experimental beams with 40mm holes at supports and center (C01, CO2, D01, and D02) were 24.74 kN and 31.64 kN respectively, while the average actual shear capacity for the control beams (E01 and E02) was 31.9 kN. The estimated ultimate load is 9.03% greater than the average actual ultimate load for slender beams E0. For beams A0, the estimated ultimate load is 38.90% greater than the actual ultimate load, while for beams B0, the estimated ultimate load is 11.22% greater than the actual ultimate load. Also for beams C0, the estimated ultimate load is 29.45% greater than the actual ultimate load, while for beams D0, the estimated ultimate load is 9.77% greater than the actual ultimate load. The estimated shear capacity is 43.87% greater than the average actual shear capacity for slender beams E0. For beams A0, the estimated shear capacity is 54.16% greater than the actual shear capacity, while for beams B0, the estimated shear capacity is 33.41% greater than the actual shear capacity. Also for beams C0, the estimated shear capacity is 47.08% greater than the actual shear capacity, while for beams D0, the estimated shear capacity is 32.32% greater than the actual shear capacity. Also for beams E0, the estimated shear capacity is 31.76% greater than the actual shear capacity. It is recommended that service holes should be located at the center of the beam as practicable as possible