A prestressed hollowcore (PHC) slab (Figure 1.1) is a precast prestressed concrete slab typically used in the construction of floors or roofs in multi-story apartment buildings. They are also popular to be used for bridge decks (especially the longspan ones) and wall panels. A PHC slab is produced on casting beds. First, arrange the prestressing strands along the bed according to the predetermined tension value. Second, move the slab extruder to the bed, which will complete six steps at one time. They include extruding concrete for bottom, slab ribs and panels; compacting concrete; moulding hollowcore; moulding slab edge for locking key and exiting. The PHC slabs are then cured under appropriate temperature and moisture condition for a period of time (usually 28 days). Finally, it can be cut and moved out of the production line.
Prestressed HollowCore (PHC) slabs were first introduced as a structural element in early 1950s (Wijesundara et al., 2012). PHC slab design reduces the weight and the cost due to continuous voids along the span length. The prestressing strands combined with high depth/weight ratio increases the flexural capacity of PHC slabs, allowing for a longer span and higher live loads. Moreover, due to the hollow cores, PHC slabs have excellent fire resistance and heat transfer performance. Likewise, the cores inside the slabs are a practical place to install electricity and plumbing work without the need for adding a ceiling. Furthermore, the PHC slab system is an environmentally friendly construction element as it reduces the waste and noise of cast in place concrete since it is being casted in a manufactory. PHC slabs are well known for their ease and fast erection on site, which saves both time and cost. As precast elements, PHC slabs are available in different sizes ranging from 150 mm to 420 mm deep, up to 2400 mm wide, and up to 20000 mm long (Yang, 1994). Due to their design benefits, PHC slabs are usually used in repeated floors of industrial, residential and commercial buildings.
ABSTRACT: A hollowcore slab is a precast prestressed concrete member with continuous voids provided to reduce weight and cost. They are primarily used as a floor deck system in residential and commercial buildings as well as in parking structures because they are economical, have good fire resistance and sound insulation properties, and are capable of spanning long distances with relatively small depths. Structurally, a hollowcore slab provides the efficiency of a prestressed member for load capacity, span range, and deflection control. Hollowcoreslabs can make use of prestressing strands, which allow slabs with depths between 150 and 260 mm to span over 9 meters. When used in buildings, several hollowcoreslabs are placed next to each other to form a continuous floor system. The small gap that is left between each slab is usually filled with a non-shrink grout. To give the floor a smooth finished surface, a topping slab overlay, typically 5cm deep is poured on the top surface of the hollowcoreslabs. The design concepts, manufacture and the erection techniques of Hollowcoreslabs are discussed in detail
Guadeset al. 12 conducted an experimental investigation to characterise the mechanical properties of square pultruded sections (100 mm x 100 mm) using both coupon and full – scale specimens. Although, there was a good agreement between the coupon and full-scale results for single spanbeams, the effect of shear deformation on the behaviour of the pultruded profiles was neglected as the beam considered in sufficiently long. Bank 13 indicated that the effect of shear on thin walled FRP sections is very significant especially for shorter beams and should be considered in determining the elastic properties of composite material. In support of this, Bank 13 and Neto and Rovere 14 conducted experiments using full-scale sections to determine the flexural (E) and shear (G) modulus of FRP compositebeams. In both situations, three – point bending tests were used to characterise the behaviour of beams with different spans. Even though same test procedure and almost similar section properties were used in both research, there was a huge difference between the calculated E/G ratios as Bank 13 determined the elastic modulus based on Timoshenko Beam Theory while Neto and Rovere 14 used the graphical (simultaneous) test method. Mottram 15 stated that the sensitivity of the graphical method in determining the slope (of the regression line through the data points) can lead to a significant change in the E and G calculations. As a result, there is a need to revisit the graphical method used to find the flexural and shear modulus.
Since the early eighties of twenty century, the slab cross-sections with non-cir- cular voids have become commonly used gradually; as an easy and quick con- struction technique. Precastslabs become widely used end of twenty century to get quick construction with high quality. These deeper precast prestressed hol- low slab units are increasingly used in the industrial buildings and office build- ings where large spans of open parking spaces on ground floors are provided with columns spacing modules from 10 m to 17 m. As a consequence the deeper hollowcoreslabs are designed to resist higher loads and to support the longer span with minimum own weight of slabs. A hollowcore slab is a precast, pre- stressing concrete member with continuous voids being provided to reduce weight and cost. These slabs which are made of high-strength concrete are pre- fabricated concrete members with large hollow proportions. In practice, they are interconnected after assembling them through a joint grouting compound. On the contrary to the conventional concrete members, the prestressed hollow-core concrete slabs have many advantages, such as saving the material, speed of in- stallation, lower building costs, moreover ensuring consistent quality levels, good fire resistance, and sound insulation properties. This is addition to its ca- pability of spanning long distances with relative small depths. Hollowcoreslabs can make use of prestressing strands, which allows the slabs; their depths ap- proximating between 400 and 500 mm, in order to span 14 up to 18 meters in standard widths of 900 mm and 1200 mm which are more common in the mar- ket  .
best efficiency for a single project is obtained if slab requirements are repetitive. In the present study, the advantages of prestressed hollowcore slab elements, for construction of the floor slabs of four story building, is shown by making cost comparison between the precast beam-slab system and pre-stressed hollowcore slab system. For this purpose, the same span length is chosen for the two slab systems. These elements are designed for loads they should sustain when used in the construction of slabs. Finally cost comparison is made between the two systems of slab construction. The cost comparison showed that the prestressed hollowcore slab system of construction is more economical and faster than the precast beam-slab system.
Loading: To simulate the model behaviour in same way as experimental, boundary conditions have been applied at points where the supports and loadings exist. The boundary conditions that have applied experimentally are shown in Figure 14. The same has been simulated in ANSYS with displacement restrained in the UY, and UZ directions for nodes in the area 50mm x 1800mm at the continuous slab support(As the supporting steel plate in the experimental setup is 50 mm wide and along full length of 1800mm of slab) and for nodes in the area 200mm x 100mm at the projected portion of the beam(As a steel plate provided at 200x100mm portion of beam extension).By doing this, the specimen will be allowed to rotate at the support. In the experiment slab load 0f 2 kN/ is applied using sand bags & UDL applied on beam portion using hydraulic jack with incremental loading. The same has been simulated in ANSYS with a live load of 2 kN/ applied in the form of pressure load on the areas of slab portion. In order to simulate the wall load on the beam portion of the specimen, the UDL that was applied in experimental work is converted into an area load. That area load is applied as pressure load on the beam portion only. The boundary conditions simulated in ANSYS are shown in Figure 15 & 16.
ductility of UHP-FRC limits the allowable maximum amount of longitudinal reinforcement, which in turn leads to limited flexural capacity of the members. Conventional reinforced concrete members are designed with a smaller amount of reinforcement to meet tension-controlled behavior. This design approach in turn leads to 1) a small ultimate flexural capacity, 2) a large amount of cracking and wider crack widths under service loads, which lead to a reduced member stiffness, 3) cracks that are less likely to close after overloading, 4) a small compression zone depth that allows cracks to propagate deeply, which further reduces the stiffness, 5) large strains in rebars, which reduce aggregate interlock and shear strength, and 6) considerable yielding of rebars, which causes bond deterioration. Contrary to the conventional design concept, a new ductile- concrete strong-reinforcement (DCSR) design concept is investigated in this study. A maximum useable compressive strain of 0.015 is considered for UHP-FRC, which allows a concrete member to maintain tension-controlled behavior while using a high amount of steel rebars. Accordingly, the flexural capacity of the section increases. This approach allows the UHP-FRC’s high compressive strength to be effectively utilized in the compression zone. The synergistic interaction of strong steel and tensile strength of UHP-FRC considerably increases the cracking resistance of the member. In addition, the number and size of initial microcracks are limited due to the strong bridging effect of a high amount of steel. Therefore, the member maintains its stiffness and small deflection under service loads. This feature permits eliminating prestressing in bridge girders, where an uncracked section is desired under service loads. Besides experimental evidence, a prototype single-span 250-ft long non-prestressed UHP-FRC decked bulb-tee (DBT) girder was designed using the DCSR concept. Finite element analysis with AASHTO loading confirms that the new UHP-FRC girder satisfies code requirements. The experimental and analytical results show that conventional precast prestressed concrete girders can be replaced by the new non- prestressed decked UHP-FRC girders.
The density of the NT Core follows a similar trend to the mechanical properties, as the four independent variables are increased (Table 3). The density of the core is also dominated by the applied pressure during processing, which increases the mechanical inter-locking and reduces the free-space between the salt particles. The density of the core in- creases by 20% as the pressure is increased from 55 bar to 170 bar. Reducing the void content reduces the likelihood of undesirable resin penetration into the core during the composite moulding process, re- ducing the amount of residual material left within the composite part. Resin wicking into the core also increases the risk of dry spots forming in the composite laminate if a pre-impregnated ﬁbre system is used, as the reinforcing ﬁbres become starved of resin. Density calculations in- dicate that the average residual porosity of NT Cores pressed at tem- peratures higher than 150 °C and pressures below 170 bar is approxi- mately 10%, which is likely to be interconnected at this level. The target porosity level for avoiding resin in ﬁ ltration into the core is 7% according to . It may therefore be diﬃcult to avoid resin Fig. 5. DSC proﬁle of trehalose from 20 °C to 230 °C (heating rate 5 °C/min).
ABSTRACT: Aerodynamic stability of a proposed Cable Stayed Prestressed Concrete Bridge of span 480 m under wind loads have been studied. Flutter and buffeting responses due to wind loads was investigated on a sectional mode to the scale of 1:200. The model was tested in a wind tunnel for two values of structural damping (0.03 and 0.06) in both torsional and vertical motions with different combinations of live loads at the ratio of frequencies of torsional and vertical oscillations is equals to 1.2. The model exhibited coupled vertical and torsional oscillations in wind. In addition, another uncoupled mode in the form of rolling oscillation about the longitudinal axis of the tunnel was also consistently observed. This type of oscillation has not been reported in the literature and is believed to be due to the overtone flexural oscillation of the main span of the bridge. After trying out several curative measures, it was found that provision of small holes in the bottom of the deck, controlled the vertical and rolling oscillations. The test results were compared with the theoretical (design) values and conclusions drawn for predicting flutter and buffeting responses due to wind loads.
While sandwich composite construction has some great benefits, the behaviour of sandwich structures containing damage is much more complex and one of the major factors limiting the optimum usage of them. Due to complex manufacturing methods, composite sandwiches can contain a variety of defects. A composite sandwich is basically made of three components; a top skin, a middle core and a bottom skin. Sandwich structure relies on the adhesive bond between the skins (also called face- sheets) and core for its overall stability and consistency. A region where there is no bond is called a debond. Skin-core debonding (hereinafter called ‘debonding’) arises as a result of manufacturing defects when a small region between the face sheet and the core has not been adequately bonded or during handling or under service conditions such as impact loading. In real structures, depending on the loading conditions, this debond may propagate creating larger debonding areas, and in fibre compositebeams, this can result in debonding occurring across the full width of the beam, which may cause changes to the free vibration behaviour in addition to the strength degradation. When the natural frequency of the debonded structure is close to its working frequency, resonance could happen, which may lead to excessive vibrations and failure of the structure. Debonds are inherent potential cause for the structural failures in adhesively bonded composite structures (Abrate 1997). It can cause failure of the sandwich structure under loads significantly lower than those for a fully bonded one.
the engineer, Emad Darwish (2,3).The beams on the scheme were classified according to the architectural plan according to their initial arithmetic lengths, the dimensions of which were taken from the axes and from whom we proved those dimensions finally after conducting the necessary investigations and the dimen- sions of the main intermediate beams m and the dimen- sions of the main peripheral beams m and the dimen- sions of the secondary beams. On the same previous primary data, all loads affecting the linear meter are calculated from the main beams and the loads are: Weight of covering slab - Weight of floors - Wall weight if any - Weight of live loads if any - Self-weight differ- ence – Nerve (Rib) reaction. After the structural design process, the reinforcing steel for the Horde slab beams was chosen according to the book Reinforced concrete (4) as in Table 4.
Hollowcoreprecast pre-stressed concrete slabs are recently being used as the floors and roofs for many multistoried structures like office buildings, residential dwellings, educational building and other commercial buildings. This method of construction reduces the overall weight of the building, increases ease in construction, provides better thermal as well as acoustic insulation properties and are highly fire resistant. One of the biggest advantages is the faster rate of construction as compared to the conventional reinforced cement concrete method.
The displacement controlled distributed loading began after the topping slab was added to the model. At this stage, the hollowcore slab had an initial upward camber of approximately 0.1 inches (2.54 mm) due to the eccentric prestressing force and self weight. As more displacement was applied to the model, the interface link elements resisted an increasing amount of horizontal shear stress. Interface failure would occur as a critical load was reached, which was in equilibrium with a prescribed displacement. At the onset of interface failure, the magnitude of compressive stress that the topping slab was capable of transferring to the hollowcore slab through horizontal shear decreased due to the failure branch of the multi-linear interface link elements. This led to a reduction in the compression force within the topping slab, a decrease in the lever arm between tension and compression, and a resulting lower flexural strength.
Abstract. This paper presents an experimental study on the fire resistance of relatively thin hollow-core concrete slabs with simple supports. A series of fire tests were conducted according to ISO 834 standard on nine hollow-core concrete slab specimens with thickness not exceeding 150 mm. The key parameters investigated are the heating duration, slab thickness and load ratio. Based on the test results, it has been found that the fire- resistance ratings of all the tested specimens fall below the specified requirements in the current building regulations of Thailand. The level of concrete spalling on the fire-exposed surface increases with the heating duration. It has also been found that the fire resistance of thicker hollow-core concrete slabs may be lower, even when smaller values of maximum vertical deflection are observed during the heating period. Furthermore, a higher load ratio leads to a more rapid collapse of the tested specimen. The experimental results suggest the necessity of supplementary means of fire protection for these slabs in practical building construction.
Classical beam theory for reinforced and prestressed concrete design is mainly based on linear elastic models, which assumes that plane sections remain plane throughout the loading history. Because of this, the classical beam theory is not capable of dealing with problems where material non-linearity and/or geometric non-linearity exist. Some reinforced concrete T-beams were tested at Empa Materials Science and Technology (Deuring ). The deflection and the failure mode of the beams were analysed using the classical beam theory. Results show that in general the load-deflection curves could be predicted by the classical theory with reasonable accuracy. However, while it was predicted by the classical theory that the beams would fail in tension, such a phenomenon was not observed on any of the beams, all the beams failed in compression. In addition,
0.003 at the ultimate load level. Appendix B provides details of the measured flexural strain profile at midspan and quarter spans for compact spandrel LG1. It was interesting to observe that the tensile strain measured at quarter span exceeded the tensile strain at midspan. This could be due to the combined effects of torsion, lateral bending, and vertical flexure near the quarter span. It was also observed that the tensile strains increased significantly towards the ultimate loading cycle indicating the formation of diagonal cracks at a load level of 200 kips. Measured strains from the PI gages mounted on the inner face of the beam near the supports shown in Figure 4-15, indicate out of plane bending. While this data is somewhat inconsistent, due to the fact that crack formations tend to be random and unpredictable, there was a clear trend of increasing strain for each load increment. In addition, at failure both the vertically oriented gages registered strains equal to or above 0.002, indicative that the steel in the inner (front) face of the beam yielded at certain locations.
Transfer length results from this research program showed no clear difference or correlations be- tween live-end and dead-end transfer lengths for any of the beams tested. This is attributed to the gradual release of the prestressing force (Staton et al. 2009). Therefore, the average transfer length for a beam series is calculated using all of the measurements from both ends of the beam. For the beams series N40-16 and N40-12, both series had the same concrete compressive strength and prestressing stress with different bar diameters. The average transfer length for the N40-16 series was 276 mm (about 17.3d b ) with a standard deviation of 14 mm, while the average transfer length for the N40-12 series was 224 mm (about 18.6d b ) with a standard deviation of 13 mm. This shows that the value of the transfer length decreased by about 19% when the bar diam- eter decreased from 16mm to 12mm. This agrees reasonably with the literature where it is re- ported that the transfer length is directly proportional to the diameter of the prestressed bar. Comparing the results of the beams series N40-16 and H40-16 shows the effect of concrete com- pressive strength on the transfer length of prestressed GFRP bars. The concrete compressive strength in the N40-16 series at the time of release was about 31 MPa while the H40-16 had a concrete compressive strength of about 71 MPa at the time of release. The average transfer length was found to be about 188 mm (about 11.8d b ) with a standard deviation of 13 mm for the H40-16 series compared to the 276 mm transfer length for the N40-16 series. This indicates that the transfer length of prestressed GFRP bars decreased by about 32% when the concrete com- pressive strength at the time of release increased by 56%. The concrete strength is reported in the literature to decrease the transfer length of CFRP bars when it increases. For AFRP, it was re- ported by several researchers (Nanni et al. (1992), Zou (2003)) that concrete strength had a min- imal effect on the transfer length of AFRP bars. This can be attributed to the short transfer length values measured for the AFRP bars. Although, the modulus of elasticity of AFRP is similar to that of GFRP, the diameter of the AFRP bars used in the literature (normally <=8mm) was smaller than the diameters of GFRP bars used in this study. The larger diameter of GFRP bars resulted in longer measured transfer lengths which allowed the effect of concrete strength on the transfer length to be more obviously observed.
Abstract: Aluminium sandwich construction has been recognized as of promising concept for structural design of light weight transportation systems such as aircraft high speed trains and fast ships. The aim of the present study is to investigate strength characteristics of aluminium sandwich panels with aluminium corrugated core experimentally. A series of crushing and bending test is carried out on corrugated core sandwich panel. The comparison of results is done based on the parameters viz. no of layers and patterns of perforated sheets. The structural failure characteristics of corrugated core sandwich panels are discussed. The test data developed are documented.