Precast Hollow-Block Reinforced Concrete Bearing Walls Al-Tuhami AbuZeid Al-Tuhami AbdAllah

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1 Precast Hollow-Block Reinforced Concrete Bearing Walls l-tuhami buzeid l-tuhami bdllah bstract This paper presents a new method and technique for enhancing the behavior of sandwich panel bearing walls under in-plane loads. The suggested technique is based on presenting a complete interaction wall panel in the two directions, by using fully interacting vertical and horizontal concrete ribs along with the traditional two parallel concrete layers. Each wall panel consists of light weight filling material blocks, two parallel reinforced concrete layers and reinforced concrete ribs. The longitudinal reinforcement of the ribs is slightly protruded outside the wall panel to be used for assembling the reinforced concrete walls and slabs in the building construction site. The filling material blocks may be polystyrene-foam or any light weight filler material having good thermal and sound insulation and allows for concreting without crushing. In the present work, experimental study and technical details of the suggested technique along with those of the traditional sandwich panels are presented. The experimental work is conducted on full scale specimens to verify the applicability and efficiency of the proposed method. Results indicated that the ultimate loads, failure modes, and load deflection relationships of the proposed walls are greatly improved by using the suggested technique. Index Terms Precast Concrete, Hollow-Blocks, Bearing Walls. I. INTRODUCTION The housing problem occupies a leading position in the list of social and economic priorities in many developing countries. Thus, there is an urgent need for alternative systems to fulfill the rapid expansion of the construction demand in terms of quality, affordability, strength properties and environmental aspects. Precast concrete structures with load bearing wall panels allows for a high level of quality control, quick enclosure of a structure, saves manpower, allow for large spans between supports, used as shear walls, more durable than brick walls, and eliminate the need for a skeleton reinforced concrete structure will infill brick walls. The precast concrete sandwich panels (SWPs) have all of the desirable characteristics of a normal precast concrete wall panel. In addition, the insulation provides superior energy performance, moisture protection, and being light weight. The hard surface on the inside and outside of the sandwich panel provides resistance to forklift damage, theft, vandalism and a finished product requiring no further treatment if desired [3]. The concrete sandwich panel is composed of two layers of concrete separated by a continuous layer of insulation. The concrete layers are connected together through members that pass through the insulation blocks into the concrete layers and transmit forces between the two layers. The forces are transmitted between the two concrete layers by metal trusses or ties. These trusses or ties are capable of transmitting forces in a number of different directions such as perpendicular to the planes of the concrete layers or at angles to those planes but in the plane of the metal trusses. Steel mesh Concrete layer Polystyrine foam Diagonal Fig. 1 Isometric view of sandwich wall panel cross-section with tie connectors between the concrete layers Photos 1, 2: SWP during construction and its layers, after [15]. Fig. 1 shows the isometric view of sandwich wall panel (SWP) cross-section with tie connectors between the concrete layers, while Photo 1,2 show the SWP during construction and its layers [1] [9]. The metal ties transfers part of the heat from one concrete layer to the other through the metal. Glass fiber-reinforced polymer ties are developed by Nebraska-Lincoln (1995) to produce ties with good thermal properties. For all the above techniques, the level of connection controls the forces transmitted between the two concrete layers which referred to composite, no composite or semi-composite panels. In the present work, the connection between the two 463

2 concrete layers is done by reinforced concrete ribs. This study presents a method, technique and experimental study of pre-cast reinforced concrete hollow block walls panels [10]- [13]. The main scope of the current research is presenting a complete interaction wall panel in the two directions, by using fully interacting concrete ribs along with the traditional two parallel concrete layers. The full interaction is assured through presenting a different system of vertical and horizontal elements all connected together with concrete layers allowing for the loads and consequently straining actions to be distributed in two directions. This is a superior advantage over the above-mentioned techniques in which single blocks are connected by horizontal or inclined ties or trusses only. The full-scale experimental work results showed a very good enhancement in the failure mode and the ultimate load capacity over the traditional panel walls. d) The designed concrete is poured in the mold for the first layer. Placing the foam (polystyrene) or filler blocks material in place between the ribs and above the first concrete layer, Photo 4. e) Placing the other reinforcement mesh and attaching it with the other side of the rib reinforcement. f) The longitudinal reinforcement of the ribs would be slightly protruded outside the wall panel to be used for assembling the reinforced concrete walls with other walls or slabs in the construction site. g) The designed concrete is poured in the mold to full fill the mold and make the concrete cover with the required thickness. h) The longitudinal reinforcement of the ribs is slightly protruded outside the wall panel to be used for assembling the reinforced concrete walls and slabs in the building construction site, as shown in Fig. 3. II. MNUFCTURING DETILS It should be noted that, the following procedure is a part of Egyptian patent bending number 1449/2009. a) Preparing the reinforced wire meshes with the required panel dimensions. b) Preparing the steel reinforcement for ribs which contains the longitudinal reinforcement and stirrups. Wall panel 2 Stirrups Longitudinal reinforcement of corner ribs 4 8mm protruded reinforcement of longitudinal ribs Wall panel 3 Stirrups Reinforcement of HL or VL ribs Wire mesh Temporary form Temporary form Fisher bolt Wall panel 1 Fig. 2: Rib reinforcement attached with one side wire mesh. Fig. 3: ssembling of three perpendicular walls. Foam Blocks First concrete layer Reinforcement of horizontal ribs Reinforcement of vertical ribs Photo 3: reinforcement of wall panel comprise of ribs and wire mesh, the panel mold contain door spacing. Photo 4: showing placing the blocks of filler material in place between the ribs and above the first concrete layer. c) rrange the rib reinforcement and attaching or fixing with the one side wire meshes Fig. 2, Photo

3 III. THE TECHNIQUE FETURES lthough the above description contains much specificity, these should not be construed as limiting the scope of the present technique, but as merely providing illustrations of some of the presently preferred embodiments of this technique. For example, the technique can cover the slabs and retaining walls. In addition, the technique could be easily used with other traditional skeleton columns and slabs buildings to contain bearing walls. Moreover, the reinforcement used for ribs, meshes and tie connectors could be of steel or other newly introduced materials such as glass or carbon reinforced polymers. IV. EXPERIMENTL WORK This part presents an experimental study to verify the structural behavior of the introduced technique for the pre-cast hollow block bearing walls. Testes are carried out on two full-scale wall specimens having a concrete category of about 25 N/mm 2 after 28 days. One specimen is taken as a reference wall specimen and the others are made to study the effect of the structural performance of the suggested technique. The reference specimen panel wall W1, as shown in Fig. 4, composed of the followings; a) a polystyrene core plate of 8 cm thickness with density of 15 kg/m3, b) two reinforced concrete layers with of 3 cm thickness each. The second wall specimen W2 (Fig. 5) consists of light weight filling material blocks (polystyrene foam with density of 15 kg/m3), two parallel reinforced concrete layers and reinforced concrete ribs. For the two test specimens, the reinforcement of each concrete layer is electro-welded steel wire meshes formed by 2.7 mm diameter wire with horizontal and vertical spacing of about 70 mm. For the reference wall specimen W1, the two parallel steel meshes are connected by ties from steel wires of 3 mm diameter. The number of ties is 55 per square meter of the wall panel. The structural capacity of the panel wall is given by the concrete layers (concrete and steel). It should be noted that, there are not any tie connectors used between the two parallel concrete layers in specimen wall W2. The ultimate tensile strength of the meshes of the panel walls W1, W2 is 500 MPa. The reinforcement details and dimensions of the wall specimens W1 and W2 are shown in Fig. 4 and 5 respectively. Ordinary Portland cement, siliceous sand and fine grained dolomite fragments are used in the concrete mix. The used dolomite fragments are 90% passing sieve size 4.75mm, and the remaining 10% are passing sieve size 10mm. ll the tested dolomite fragments are retained on sieve size 2.18 mm. The absolute volume method was used in designing the concrete mix. The following concrete mix proportions were adopted in this study:. Test Setup In order to ensure that the applied vertical axial load is uniformly distributed over the wall, the following procedures are used: 1) The specimens are provided with upper and lower horizontal ribs. Each rib is prepared with seven uniformly distributed holes, over its length, to provide lateral confinement. 2) Two angles are placed and affixed for each upper and lower rib. These angles are having holes coinciding with the previously installed threaded bars. 3) Threaded bars are installed in the previously prepared holes with lengths extruding outside the wall to allow for placing nuts and washers and consequently for tying the nuts to confine the upper and lower parts of the wall. This technique avoids the occurrence of local failure during loading along the panel edges. 4) Two 10 mm thick reinforced rubber sheets are placed one above and the other under the sample to ensure uniform leveling of the sample loading surface. 5) Stiff built-up steel I beam is then placed along the width of the wall sample under the load cell to ensure distributing the load uniformly. The specimens setup is shown in Photo 5. The samples are tested under vertical axial in-plane load from a hydraulic jack loading unit that transfers the acting load through the I-beam into a distributed load along the width of the wall. The load is applied incrementally with equal increments of 5 ton each. The vertical and lateral displacements are measured by two electric displacement instruments (LVDT's) installed on steel stands. For the second wall specimen W2, two strain gauges are fixed on the vertical and horizontal rib reinforcements to estimate the steel strains, while two other strain gauges are installed on the concrete at mid-height of the specimen and the other one in the upper third of the specimen height. ll the instruments are connected with Data Logger to obtain the displacement and strain data during the loading process. Photo 5: shows the specimens setup. 80 mm Sec mm Wire mesh 2.7 mm@70mm Longitudinal reinforcement of ribs 4 6mm 2400 mm Fig. 4: Reference Specimens (W1) details mm 465

4 dolomite Sand Cement Water mm Wire mesh 2.7 mm@70mm Detail B Detail 500 mm Detail B 2700 mm 4 8mm Stirrups mm Wire mesh 2.7 mm@70mm Stirrups 3.5 vertical rib Longitudinal reinforcement of ribs 4 8mm Wire mesh 2.7 mm@70mm Sec - 80 mm Detail Fig. 5: Wall skeleton without concrete; elevation, sectional plane and details of the test specimen W2 representing the suggested technique. B. nalysis of the Results The scope of the current experimental work is presenting technical details of a new technique for enhancing the behavior of traditional sandwich panels. Two full scale panels are tested, namely W1 representing the traditional sandwich panel, and W2 representing the suggested technique. The experimental work is carried out to verify the applicability and efficiency of the suggested method. The sandwich panel specimen W1 which is comprised of a polystyrene foam plate, two reinforced concrete layers connected together with a number of ties and upper and lower horizontal ribs. The cracking load started at 300 kn, in which horizontal hair cracks started to appear at mid-height of the wall specimen. Complete failure of the wall specimen took place at 400 kn load in which a total buckling displacement of 135 mm at mid-height of the wall is measured. Moreover, at failure a lateral horizontal crack took place at the lower confined rib of the wall. Such failure sequence assures that the wall is fully fixed at the upper and lower edges, simulating the actual field conditions. This failure also assures the good fixation of the lower and upper beams confined by the steel angles and under the specified confining pressure, as presented in Photo 6 and 7. The second tested wall W2 sample that represents the suggested technique is shown in Fig. 5. The cracking load started at about 600 kn, in the form of horizontal hair cracks in the lower third of the wall specimen in zone bounded by two vertical ribs, in one face only. Increasing the applied load resulted in buckling in the wire mesh at the position of these hair cracks. Continual increase in the applied load resulted in buckling in the longitudinal reinforcement lower third of the middle vertical rib accompanied by spalling of the concrete cover away from the wall. t 850 kn of loading, the dial of the load cell moves back to less than 800 kn indicating that failure occurred in the wall specimen. Increasing the load back resulted in vertical upward crack propagation around the vertical ribs and inclined cracks started to form within the two lower corner edges. Moreover, vertical and inclined cracks started to propagate upward starting from the lower corners just beside the external ribs in the lower third portion of the wall specimen only, as shown in Photos 8-10.The load versus vertical deflection of wall specimen W2 is given in Fig. 6, while comparison of the mid height for lateral buckling displacement between the sandwich panel reference specimen W1 and hollow-block reinforced concrete bearing wall specimen W2 is shown in Fig. 7. Summary of the results of walls W1 and W2 are presented in Table

5 Photo 6, 7: Elevation and side view of the reference wall specimen W1 showing horizontal cracks and the buckling failure of the specimen. Photo 9 Photo 8 Photo 10 Photo 8-10: Failure mode of ribbed panel wall W2. 7) Cracking pattern concentrated between the lower horizontal ribs. 8-9) cracks and buckling the longitudinal reinforcement of meddle and outer vertical ribs and spalling the concrete cover. 467

6 load,kn load,kn Spec. No ISSN: Dimen. mm. H l. Ribs Table 1: Summary the details of walls W1 and W2 are given. Ribs V l. Ribs F cu N/mm 2 No of ties/m Loading type Max. buckling displacement, mm Failure load Yield load kn Ultimate load kn W1 200x In-plane W2 200x In-plane Wall1 Wall deflection, mm Fig. 6: load versus vertical deflection of wall specimen W2 V. CONSTRUCTION DIFFICULTIES ND SOLUTIONS lot of difficulties arise when pouring and casting the presented wall panels. Difficulties include leveling and compacting the first concrete layer within the protruded ties, placing the light weight block materials in the presence of the ties connecting the upper and lower concrete layers. Difficulties also include consuming a long time in attaching the upper steel reinforcement mesh with the rib reinforcements and ties. This delay in time results in lower quality concrete, in addition to higher manpower cost associated with such long construction time. Due to the fact that ordinary fresh concrete, even with super-plasticizer, would not be able to fill in all the allocated lower and upper concrete zones, thus, self compacting concrete is the solution in such case. Self compacting concrete allows for the followings; assembling all the panel reinforcement skeleton and light weight material blocks before the start of concreting, and allows for the fresh concrete to fill in all the allocated zone along with eliminating the possibility of honeycombing or voids within the concrete body. The used self compacting concrete is designed to satisfy all the mix requirements with suitable coarse aggregate size. new lateral deflection, mm Fig. 7: comparison between the mid height of lateral buckling displacement for walls W1 and research is performed using self compacting concrete to overcome the problems associated with concrete casting difficulties in the current research along with the presence of ribs and their positions, and the number of ties. VI. CONCLUSION Experimental study and technical details of a new technique for enhancing the behavior of sandwich panels are presented. The reference sandwich panel specimen composed of two layers of concrete separated by a continuous layer of insulation and connected together through a number of ties that pass through the filling lightweight plate. The suggested technique specimen consists of blocks of light weight filling materials, two parallel reinforced concrete layers and reinforced concrete ribs. The vertical and horizontal ribs all connected together with concrete layers allowing for the loads and consequently straining actions to be distributed in two directions. This is a superior advantage over the traditional sandwich panels in which single blocks are connected by horizontal or inclined ties or trusses only. The results obtained from testing the reference specimen are compared with that obtained from the specimen representing a complete interaction wall panel. The full-scale experimental work results showed a very 468

7 good enhancement in the failure mode and the ultimate load capacity over the traditional panel walls. From this research, the following advantages of the suggested method can be concluded: 1) Overcoming the buckling mode of failure by minimizing the lateral displacements even under higher axial loads. 2) large increase is observed of yield and ultimate load-carrying capacities of the proposed technique specimen compared to reference sandwich panel ones. The mode of failure was changed from brittle buckling to compression failure. 3) The presence of horizontal and vertical ribs limits the formation cracks even at higher loads. The active pressure increases also the lateral confinement and enhances the mechanism of concrete confinement. CKNOWLEDGMENT Useful discussions and comments with associate professor S. S. li-eldin at the Mechanical Design and Production Department and professor T. N. Salem at the Structural Engineering Department., Faculty of Engineering, Zagazig University, Zagazig, Egypt are gratefully acknowledged. REFERENCES [1] S. Freedman, Load bearing rchitectural Precast Concrete Wall Panels, PCI Journal, V. 44, No. 5 pp , (September October), [2] C.Jagdish Nijhawan, Insulated wall panels interface shear transfer, Technical note, PCI Journal, pp , May-June [3] PCI Committee Report, State-Of-The-rt of Precast/Prestressed Sandwich Wall Panels, vol. 42 no 2, pp 1-6, March-pril1997. [4] J. Christian, and J Kosny, "Home energy", Home Energy Magazine Online November/December, [5].. Benayoune,.. Samad., bang li, D.N. Trikha, Response of precast reinforced composite sandwich panels to UTHOR BIOGRPHY uthor l-tuhami buzeid l-tuhami, PhD, P.Eng., is an associate professor at the Structural Engineering Department in the faculty of engineering at Zagzaig University in Zagzaig, Egypt, Director of Innovation and pplied Research Committee in Egyptian Engineering Syndicate. RE OF INTEREST Innovative techniques in retrofitting the reinforced concrete structures, mechanical couplers for reinforcing bars and new building systems axial loading, Journal of Construction and Building Materials, pp [6] E.. bdelfattah, Structural behavior of precast concrete sandwich panel under axial and lateral loadings, Mc.S Report, University Putra Malaysia, [7] N. Mohamad and H. M Muhammad, Testing of precast lightweight foamed concrete sandwich panel with single and double symmetrical shear truss connectors under eccentric loading, Journal of dvanced Materials Research, Vols , pp , [8] E. Losch, "Precast/prestressed concrete sandwich walls.", Structure Magazine pp pril, 2005 [9] F. Sidney, Load bearing architectural precast concrete wall panels, PCI Journal, September- October, [10] C. P. Pantelides, L. D. Reaveley, and P. W. McMullin, Design of CFRP composite connector for precast concrete elements. Journal of Reinforced Plastics and Composites, V. 22, No. 15, pp , [11] W.William, R.. David and K. T. Maher K, NU precast concrete house provides spacious and energy efficient solution for residential construction, PCI Journal, pp , May-June [12] B.. Frankl, Structural behavior of insulated precast prestressed concrete sandwich panels reinforced with CFRP grid, University of North Caroline State, Page 28, [13] H. Gleich, New carbon fiber reinforcement advances sandwich wall panels. Structure Magazine pp , pril (2007). [14] K. H. Tarek and S. H. Rizkalla, nalysis nd Design Guidelines Of Precast, Prestressed Concrete, Composite Load-Bearing Sandwich Wall Panels Reinforced with CFRP Grid, PCI Journal, Spring [15] Emmedue company manual Emmedue Panels and tools, Rev.O2 of 14/09/2004. PUBLICTIONS: Over thirty papers in Journals and Conferences PTENTS: Inventor Name: l-tuhami buzeid l-tuhami 1. Egyptian Patent No Mechanical strengthening technique, Egyptian Patent No method for strengthening the RC beams and beam-column connection using external pressure, US6,718,723 Method and pparatus for Strengthening the Concrete Elements using Pre-stressing Confinement., International Patent Classification (IPC): IPC 8 : E04C 5/16 ( ) PCT/EG2005/000014, Mechanical Reinforcing Bar Coupler Based on Bar Deformations 6. Egyptian Patent No , Egyptian Patent application No method for construction light weight environment friendly building with overall good mechanical properties