Amount Of Steel Reinforcement Research Articles

Concrete jacket construction detail effectiveness when strengthening RC columns

This paper presents an experimental investigation of the effectiveness of strengthening half height full size concrete columns by placing concrete jackets. Three alternative methods of concrete jacketing are investigated and results are compared with results from an original unstrengthened specimen and a monolithic specimen. The specimens were designed to represent typical ground floor columns of a concrete frame building. The unstrengthened column and the original columns of the strengthened specimens were designed to old 1950s Greek Codes. Poured concrete or shotcrete was used to construct the jackets of the strengthened specimens and, as performed in practice, various other construction procedures were carried out in order to evaluate if it is worth performing the procedures when considering the practical difficulties involved. These procedures involved welding the jacket stirrup ends together, placing steel dowels across the interface between the original column and the jacket in combination with welding the jacket stirrup ends together and connecting the longitudinal reinforcement bars of the original column to the longitudinal reinforcement bars of the jacket. In order to investigate the lower limit of the effectiveness of the technique, the case of no treatment at the interface between the original column and the jacket combined with the construction of a low strength cast in situ concrete jacket is examined. The same cross sectional dimensions and amount of steel reinforcement were used for the strengthened specimens and a control monolithic specimen. Earthquake simulation displacement controlled cyclic loading was used for the testing. The seismic performance of the tested specimens is compared in terms of strength, stiffness and hysteretic response. The effectiveness of properly constructing concrete jackets has been proved, as it was found that, under special conditions, an almost monolithic behaviour could be achieved. Even when the jacket was constructed with no treatment at the interface, a significant strength and stiffness increase was observed. It was also found that the failure mechanism and the observed crack patterns are influenced by the strengthening method. The separation of the jacket from the original column was obvious in the case when there was no treatment or other connection means performed at the contact interface between the column and the jacket. In addition, it was found that welding the jacket stirrup ends together stopped the longitudinal bars of the jacket from buckling.

Steel-fibre high-strength concrete prisms confined by rectangular ties under concentric compression

This paper presents results from a continuing research program that aims to investigate the behaviour of high-strength concrete columns and to recommend some design procedures to Brazilian Building Code. The specific current work deals with experimental behaviour of steel fibre high-strength concrete columns (SFHSCC) confined with low ratios of rectangular ties under concentric compression. Twenty-four small-scale SFHSCC were tested under concentric loading and their behaviour were examined and compared with the behaviour of two normal-strength concrete columns. The variables studied in this work were the concrete strength, amount of transversal reinforcement and volumetric fraction of steel fibre. The results indicated that steel fibre not only improves the columns ductility, but also avoids the premature concrete cover spalling. Further, to improve the ductility of high-strength concrete column, the used amount of steel reinforcement is the same when the confinement or steel fibre is applied.

鉄骨梁と鉄筋コンクリート柱からなる柱梁接合部の支圧破壊と耐力モデル

This paper presents a study on bearing failure of a rigid-framed joint between steel beams and reinforced concrete columns. To have a better understanding of the bearing failure, small-scaled concrete block tests were conducted under a localized bearing loading condition. The variables considered in the tests included the concrete strength, the type and amount of steel reinforcement, and the size of the loading area. The crack and failure patterns observed were similar to the ones typically seen in the beam-column joint tests. The test results indicated that all the variables substantially affected the bearing strength and deformation capability. Based on the test results, a strength model was proposed for the small-scaled" concrete blocks, consisting of three resisting elements such as direct shear resistance, and resistances due to confinement from surrounding concrete and steel reinforcement. Applying a stress block technique using the proposed model, a strength design equation was further derived for the joint bearing failure. Comparing with eighteen interior subassemblage test results, it was shown that the equation provided conservative and consistent strength estimates with proper accuracy.

An Experimental Study On Spalling Of High Strength Concrete Elements Under Fire Attack

The spalling of high strength concrete under f i e attack is discussed in this paper. Two series of f i e tests on reinforced concrete elements were carried out in order to investigate the spalling behavior and effect of spalling on the fire endurance of reinforced concrete elements. The results of the f i e tests on 30 specimens can be summarized as follows: a) the spalling is significantly affected by the water-cement ratio of the concrete, the permeability of the concrete, the amount of steel reinforcement, the f i e intensity and the age of the concrete at f i e exposure, b) the addition of polypropylene fiber into concrete is a good measure for the prevention of spalling and can improve the f i e endurance of reinforced concrete elements, c) the addition of polypropylene fiber into concrete at a ratio of Ikg polypropylene fiber per lm3 concrete reduces the depth of spalling by about 18mrn.

Structural Modeling for Reconstruction of Arch Bridge

When a 70-year-old multiarch concrete bridge was to be reconstructed by removing the deck and vertical spandrel columns down to the arch, analysis was necessary for unloading and reloading. The arch bridge, located on TH-55 over the Minnesota River, was of world-record length for such a structure when it was originally constructed in 1926 through 1928. The amount of steel reinforcement in each of the two support arches was only 32 No. 9 bars of 28.6-mm (1.125-in.) diameter. The deck, which was 18.3 m (60 ft) wide and supported at 9.1 m (30 ft) by columns, was designed as a patented panel system. This involved the use of only 250 kg (550 lb) of reinforcement in each deck panel. The slab did not possess upper reinforcement in the center areas, so removal operations could not allow the slab to cantilever in these areas. As a result of the minimal steel reinforcement in the deck and arches, removal operations needed to be planned safely and effectively. At no time during the removal process could the arches be placed in flexural stress above their very limited carrying capacity. Prospective contractors were advised of this condition and were given 2 weeks beyond the original deadline to submit bids accordingly. The proposal and plans given to each prospective contractor for bidding showed a possible deck removal method using a crane. Structural modeling by the contractor's consultant and the Minnesota Department of Transportation using Staad III finite element analysis was necessary for the contractor's bridge deck removal and replacement method. The existing slab removal and replacement with a wider, 27.4-m (90-ft) deck was successful and the bridge was reopened to traffic in October 1994.

Structural Modeling for Reconstruction of Arch Bridge

When a 70-year-old multiarch concrete bridge was to be reconstructed by removing the deck and vertical spandrel columns down to the arch, analysis was necessary for unloading and reloading. The arch bridge, located on TH-55 over the Minnesota River, was of world-record length for such a structure when it was originally constructed in 1926 through 1928. The amount of steel reinforcement in each of the two support arches was only 32 No. 9 bars of 28.6-mm (1.125-in.) diameter. The deck, which was 18.3 m (60 ft) wide and supported at 9.1 m (30 ft) by columns, was designed as a patented panel system. This involved the use of only 250 kg (550 lb) of reinforcement in each deck panel. The slab did not possess upper reinforcement in the center areas, so removal operations could not allow the slab to cantilever in these areas. As a result of the minimal steel reinforcement in the deck and arches, removal operations needed to be planned safely and effectively. At no time during the removal process could the arches be placed in flexural stress above their very limited carrying capacity. Prospective contractors were advised of this condition and were given 2 weeks beyond the original deadline to submit bids accordingly. The proposal and plans given to each prospective contractor for bidding showed a possible deck removal method using a crane. Structural modeling by the contractor's consultant and the Minnesota Department of Transportation using Staad III finite element analysis was necessary for the contractor's bridge deck removal and replacement method. The existing slab removal and replacement with a wider, 27.4-m (90-ft) deck was successful and the bridge was reopened to traffic in October 1994.

Design and construction of a segmental lining for a machine-bored tunnel: Delivery tunnel North, Lesotho highlands water project

The 21-km-long Delivery Tunnel North for the Lesotho Highlands Water Project is split into two main tunnel drives of 8 km and 11 km lengths. The tunnel is located in the sedimentary rocks of the upper Karoo series with cover of up to 350 m. The rock units comprise claystones, siltstones and sandstones. In the poorer geology, early support of the tunnel periphery is essential. The method of tunnel construction involves excavation by a TBM and the simultaneous erection of a precast concrete segmental lining that provides both rock support and a final tunnel lining. The segmental lining is designed and constructed as part of an integrated excavation/support/lining system. There are three types of segments, differentiated by the amount of steel reinforcement. The distribution of the different segment types along the tunnel, relative to the geological conditions and depth of cover, will be optimized by monitoring of the performance of the lining during the construction period. Le canal d'écoulement nord du Lesotho Highlands Water Project, long de 21 km, est divisé en deux tunnels principaux de 8 et 11 km. Ce tunnel se situe dans les roches sédimentaires des couches supérieures de Karoo, avec une couverture atteignant 350 m. Le terrain se compose de roches argileuses, de silt et de grès. Lorsque les conditions géologiques sont difficiles, il est essentiel de mettre en place un soutènement à la périphérie du tunnel. La méthode de construction utilise un TBM et la mise en place simultanée de voussoirs en béton préfabriqués, qui assurent à la fois le soutènement de la roche et le revêtement définitif du tunnel. Le revêtement en voussoirs est conçu et construit comme partie du système intégré creusement/soutènement/revêtement. Il existe trois types de voussoirs, différenciés par le volume d'armature métallique. La distribution des différents types de voussoirs le long du tunnel, en fonction des conditions géologiques et de la hauteur de couverture, sera optimisée par le contrôle des performances du revêtement au cours de la période de construction.

建設材料特集 ＡＳＲによる損傷に及ぼす鉄筋拘束の影響に関する研究

In reinforced concrete structures, the degree of deterioration due to an alkali aggregate reaction is influenced by the amount of reinforcement in the concrete, because the reinforcement restrains the expansion due to the alkali aggregate reaction. To investigate the effect of reinforcement steel on the deterioration of concrete, experimental works were made using concrete prism specimens with various amounts of steel reinforcement. Expansion and crack patterns were measured for 2 years. And the compression tests of the concrete prism specimens were caried out after 5 year's storage. Compressive strength, stress-strain relationship and Young's modulus were measured for each specimen. At the same time, acoustic emission characteristics of each specimen during compressive loading were investigated.The test results show that the deterioration of concrete due to the alkali aggregate reaction decreased extremely when the steel reinforcement ratio was more than 0.71%. One of the reasons is considered that the growth of cracks is restricted by the chemical prestress induced in the concrete with the expansion of concrete due to the alkali aggregate reaction, resulting the decrease of water supply to the inner part of concrete.

Fire Resistance of Reinforced Concrete Columns: a Parametric Study

Experimental and theoretical studies were carried out to develop general methods for the prediction of the fire resistance of reinforced concrete columns. In these studies, which were carried out jointly between the National Research Council of Canada and the Portland Cement Association, 41 columns were tested. The parameters studied included load level, amount of steel reinforcement, effective length of column, concrete strength, moisture content, area and shape of cross section, aggregate type, axial restraint of ther mal expansion and load eccentricity. The experimentally discovered effects of these parameters are discussed.