رفتار ساختاری از سیمان آهن دار-آجر پانل دال کف کامپوزیت
|کد مقاله||سال انتشار||مقاله انگلیسی||ترجمه فارسی||تعداد کلمات|
|28713||2010||7 صفحه PDF||سفارش دهید||محاسبه نشده|
Publisher : Elsevier - Science Direct (الزویر - ساینس دایرکت)
Journal : Construction and Building Materials, Volume 24, Issue 11, November 2010, Pages 2224–2230
This study introduces a semi-fabricated system for the construction of floor slab. The slab panel consists of two layers joined together using truss type shear connectors. The first layer is a precast ferrocement layer which acts initially as a formwork, while the second layer consists of bricks and mortar. Continuous truss shear connectors are used to connect the two layers. The paper experimentally investigates the structural response of ferrocement–brick composite panel under flexural load. Four full scale specimens were cast and tested under two-line loads. The study highlights the effect of shear connectors and brick layout on the overall structural response of the slab. The results in terms of load–deflection, crack pattern, strain distribution and failure loads indicate that the response of the composite slab to the flexural loading is satisfactory and can be used as a floor slab in construction sector.
Prefabricated floor is used in the construction sector in many parts of the world. It is an alternative system used to overcome the formwork problems (cost and delay in construction) in addition to getting better quality control. It was found, however, that the prefabricated elements made of reinforced concrete are very heavy and difficult to transport and construct. In addition, concrete provides low thermal insulation quality, which is desired for living quarters and shelters. Jointing connectivity is another problem observed in precast construction, which leads to somehow, a less integrated structure. To reduce these deficiencies, a large number of precast systems have recently been developed. Pessiki et al.  summarized the use of 19 different precast structural floor systems that are suitable for office building construction in different parts of the world. Thin ferrocement panels were used in floor construction for low cost housing  and  due to its low cost and good structural performance. The introduction of insulating sandwich panels increased the attractiveness of this type of construction. The panels consist of thin layers of relatively higher strength material sandwiching a thick core, of normally much weaker and lower density material ,  and . However, the high manufacturing and construction costs limit the use of precast sandwich panels in construction. The profiled sheeting–cement board composite is another recent development in the floor slab system  and . The system consists of profiled sheeting attached to a top layer of dry board by simple mechanical connectors. Lightweight concrete with a density of 1000 kg/m3 was used as an infill material to act as a sound insulator for the floor. However, one of the limitations of this system is its low stiffness which results in a large deflection and development of cracks in the finishing elements connected to the slab. Half-slab construction technique is another development in the construction of floor slab  and . The techniques employs reinforced precast floor panel that serve as permanent formwork which is composite with cast in situ concrete. Steel lattice trusses project from the top of the precast unit were used to connect the two layers and provides the unit with stiffness during erection. Again the heavy weight of the full slab and their low thermal efficiency are some of the disadvantages of the system. To develop a new floor slab system to overcome the shortcoming in the in situ concrete floor slab and existing precast floor systems is a challenging task for many researchers. As a summary, the main shortcomings in the existing systems could be one or more of the followings: • Long construction time. • Heavy weight. • Dependency on heavy equipment on job site. • Bad thermal and sound barrier. • Wastage of material • Dependency on formwork. • Does not ensure structural integrity. • Jointing problems. • High cost. This study introduces a semi-precast floor slab system; ferrocement–brick composite slab to address some of the above listed shortcomings in existing systems. The new system consists of a bottom ferrocement skin, brick masonry and in situ mortar ribs. The ferrocement layer is the precast part of the composite slab, which consists of a wire mesh and steel reinforcement, required to resist the tensile stresses. The thickness and reinforcement of this layer will depend mainly on the span of the slab. The brick layer and the in situ ribs provide the necessary resistance to the compressive forces developed due to bending. The two layers are interconnected using truss type shear connectors (see Fig. 1).The advantages of this system, amongst others, are its relatively lighter weight compared to R.C which will reduce the load transferred to the beams/walls. The masonry bricks act as light (especially voided brick), natural, cheap effective insulation material and at the same time resisting partially the compression forces developed due to bending of the composite. On site, the construction of the composite slab does not require heavy equipments to handle the ferrocement layer. Furthermore, the construction does not need any formwork since the bottom layer of ferrocement is a precast unit that can be easily fixed in position, using simple crane, to provide a platform that acts as a formwork for the brick layer and the in situ concrete ribs. However, laying the brick might be labour intensive job especially in countries where the cost of labour is high. Alternatively, the masonry brick may be laid during casting the ferrocement layer in the factory to reduce the need for intensive labour. The cold joint problem usually observed in precast construction could be eliminated in this system. The floor slab units together with the supporting beams might be integrated during casting of the in situ mortar ribs. This experimental study is limited to investigate the structural performance of one way ferrocement–brick composite slab subjected to two-lines loading. The study highlights the effects of bricks layout and shear connectors layout on its overall structural response in terms of load–deflection characteristic, ductility, strain distribution, composite action and failure load.
نتیجه گیری انگلیسی
This paper introduces a semi-fabricated composite slab and investigates its structural behaviour under flexural load. The composite slab consists of two layers joined together using truss type shear connectors. The first layer is a precast ferrocement which acts initially as a formwork, while the second layer consisting of bricks and mortar. The test results indicated that the slab can resist an average bending moment of 15 kN m/m. The ductility ratios observed are more than 2 and this is associated with large deformation and cracks. The cracking load observed is about 30% of the ultimate failure load and their patterns are similar to those observed in a typical reinforced concrete one way slab. The specimens with discontinuous brick layout and three trusses type shear connector layout show better structural performance in terms of ductility compared to the specimens with continuous brick layout and two shear connectors. The transverse ribs (in discontinuous brick layout) only enhance the ductility of the slab compared with the specimen without transverse ribs (continuous brick layout). The experimental failure loads especially for the slab specimens with triple shear connectors were found to be higher than those estimated analytically. From the distribution of strain across the depth of the slab, the two layers are acting initially in full composite manner and the shear connecter used is capable of integrating both layers. However, before failure, the two layers start to separate at the mid span by forming a horizontal longitudinal crack. For better response, the shear connection needs to be modified to ensure the full integrity at high flexural load. The predicted ultimate load using BS8110 were found to be compatible with those obtained experimentally. However when considering the material safety factor in the design; BS 8110 may provide a conservative design for the composite slab.