Punching Shear

In this paper thus to discuss about the economic product in the sense of aesthetics and more increased performance. So, concrete is a unique material with low in tensile forces. With shear of the structure may not obviously sustain by the materials as with the design. Accordingly with the less tensile force sustainability of concrete may also resist from its compression force as a result of shear occurs on a degree of angle with the compression and tension. In the same way increased concrete strength may resist a certain amount of shear. With increased yield strength of concrete using reinforcement bars that makes more resistance to shear. But still with the complexity of design may need more shear to be resisted with section. In this way longitudinal reinforcement are provided as shear reinforcement and main steel bars will carry the sagging or buckling loads. Thus still in some cases compression reinforcement also provided to a complex section so shear provision is more rather lower than without the compression members. The executive innovation on this the (design of flat slabs, bases) where and which to be constructed without a beam parallel connecting and or with large sectional loadings. With this case columns are being cracked along its column slab connection perimeter with increased loadings as a result of less connection from the rigid connections. This known phenomenon of punching shear capability of a section are investigated with EC2 manual and research based to introduce the shear capability to a section and to investigate innovative ideas to fine-tune the knowledge in designing and retrofitting works. But punching shear methods evenly applies in cases of construction of post-tensioned, High Strength Concrete Designing. Literature on Ultra High Performance Fiber Reinforced Concrete (UHPFRC) states the impotence on punching shear but less than HSC.

The standard design method (classical method) for reinforced concrete rectangular footings is: First, a dimension is proposed and should comply with the allowable stresses; subsequently, the effective depth is obtained from the maximum moment and is checked against the bending shear and the punching shear until, it complies with these conditions and, then, steel reinforcement is obtained, but it is not guarantee that the minimum cost will be obtained. This paper shows an optimal design for reinforced concrete rectangular footings using the new model. A numerical experimentation is presented to show the model capability to estimate the minimum cost design of the materials used for a rectangular footing that supports an axial load and moments in two directions in accordance to the building code requirements for structural concrete and commentary (ACI 318-13). Also, a comparison is made between the optimal design and current design for rectangular footings. The solutions show that the ...

The paper describes the quasi-static and dynamic experimental methods used to examine the confined shear strength of an Ultra-High Performance Concrete, with and without the presence of steel fibers in the concrete composition. The experimental setup that employs a hydraulic press allows investigating the concrete shear strength under quasi-static loading regime while dynamic shear strength is characterized by subjecting concrete samples to dynamic loading through a modified Split Hopkinson Pressure Bar set-up. Both methods are based on a so called Punch Through Shear (PTS) test with a well-instrumented aluminum-alloy passive confinement ring that allows measuring the change of radial stress in the shear ligament throughout the test. First, four equally distributed radial notches have been performed on the concrete samples in order to deduce the radial stress in the shear ligament by suppressing self-confinement of the sample peripheral part. However, by analyzing the strain gauge data obtained from the confinement ring, it has been noticed that these were insufficient, especially for fiber-reinforced samples, resulting in subsequently practicing eight radial notches through the peripheral part of the samples. The results obtained from both procedures in addition to post-mortem observations are reported and discussed. It is concluded that the apparent increase of shear strength under dynamic loading compared to the quasi-static response is the consequence of higher radial confinement stresses at high strain-rates that results from an alteration of fracturing in mode I prior to mode II cracking in the ligament.

Punching shear is a conspicuous phenomenon of fracture mechanism in R.C Flat slab. To meet high shear and flexural demand at critical shear zones of column supports or point loads of flats slabs, the design codes proposed to construct Column heads (capital) and Slab drops against punching shear failure. But this may lead to decrease head clearance and increase of construction cost. To optimise the slab geometry at critical sections of punching shear zones, an experimental programme conducted on three full scale R.C flat plate slabs (NSF, WSF1, WSF2) constituted with different shear resistant elements(steel fibres and headed shear studs) used in punching shear zone. The flat slabs configurated by NSF is "Flat slab using conventional shear reinforcement bars, and WSF1 is "Flat slab using steel fibre concrete in shear zone and the rest of slab with conventional reinforcement" and WSF2 is "Flat slab with combination of steel fibre reinforcement and shear studs used in punching shear zone only and the rest of slab with conventional reinforcement. Random oriented hooked steel fibres of 1.5% volume fraction used for implicit strengthening of concrete at critical punching shear zone. The test parameters considered in this study are shear performance, load capacity, stiffness degradation, energy dissipation, and crack pattern. The test results indicated that, use of steel fibres and shear studs in critical punching shear zone of flat slab is significantly improves punching resistance mechanism, and load carrying capacity of flat slab (WSF2). Further the punching shear failure at ultimate load was observed by ductile mode with good energy dissipation.

This paper presents results of tests on eight reinforced concrete slab-column connections without and with shear reinforcement under
monotonic concentric and eccentric loading. The slabs were square, with sides of 2.5 m, 180 mm thick, and were centrally supported on square column stubs with sides of 300 mm. The slabs were cast with concrete with a mean compressive strength of 49 MPa, with constant flexural reinforcement ratio (1.5%) and with different amounts of double-headed studs as shear reinforcement. All the slabs failed by punching shear and their flexural and shear responses, as well as their ultimate punching strengths, are described and discussed by comparing the experimental observations with theoretical results obtained following the recommendations presented by ACI 318, Eurocode 2 and fib Model Code 2010.

Meningkatnya permintaan produk dari konsumen membuat aktifitas
produksi padat, namun disisi lain ada beberapa permasalahan pada produktifitas yang belum terselesaikan membuat aktifitas produksi terhambat dan harus menambah jam kerja secara berkelanjutan. Tujuan dari penelitian ini adalah untuk mengetahui pengaruh hardness material kuningan dan clearance pada progressive die terhadap kualitas produk kunci serta menentukan clearance yang optimal untuk proses produksi. Penelitian ini penulis menggunakan metode eksperimental suguhan untuk mengkaji sebab akibat dalam keadaan yang tidak memungkinkan,
dengan dilakukan pembagian menjadi dua bagian, yaitu kelompok treatment dan kelompok kontrol. Penelitian menggunakan variasi kekerasan material kuningansebagai kelompok treatment dan variasi clearance progressive die sebagai kelompok kontrol, material die menggunakan SKD11 yang sebelumnya dipanaskan agar memiliki kekerasan yang tinggi serta quenching dengan teknik modusi agar
memiliki kerapatan yang baik agar lebih mudah proses analisa pada die. Pengujian dilakukan menggunakan progressive die. Pengukuran ketinggian burr diukur dengan dial indicator. Hasil dari penelitian adalah semakin kecil clearance maka akan semakin besar burr yang dihasilkan, semakin besar clearance maka akan menghasilkan burr yang semakin besar, akan tetapi semakin kecil clearance dengan hardness material yang tinggi maka semakin kecil burr yang dihasilkan namun visual kurang baik untuk pemakaian jangka panjang, sedangkan semakin
lebar clearance dengan hardness material lembek maka semakin kecil burr yang dihasilkan, namun terlalu lebar clearance dengan hilangnya burr samping tetapi akan timbul potongan tidak sempurna pada tekstur potongan. Besarnya gaya yang dibutuhkan untuk memotong part adalah minimal 77,3 ton.

Twelve slabs, 11 of which contained double-headed studs as shear reinforcement, were tested supported by central column and loaded concentrically. Their behavior is described in terms of deflections, rotations, strains of the concrete close to the column, strains of the flexural reinforcement across the slab width, and strains of the studs. All failures were by punching, in most cases within the shear reinforced region. The treatments of punching resistance in ACI 318, Eurocode 2 (EC2), and the critical shear crack theory (CSCT) are described, and their predictions are compared with the results of the present tests and 39 others from the literature. The accuracy of predictions improves from ACI 318 to EC2 to CSCT—that is, with increasing complexity. However, the CSCT assumptions about behavior are not well supported by the experimental observations.

This paper presents a comparative study for the design of reinforced concrete isolated footings that are rectangular or circular in shape and
subjected to axial load and moments in two directions using new models to obtain the most economical footing. The new models take into
account the real soil pressure acting on contact surface of the footing and this pressure is different in all the contact area, with a linear
variation, this pressure is presented in terms of the axial load, the larger moment around the “X” axis and the smaller moment around the
“Y” axis, where the centroidal axes are “X” and “Y” of the footing. The main part of this research is to show the differences between the
two models. Results show that the circular footings are more economical compared to the rectangular footings. Therefore, the new model
for the design of circular isolated footings should be used, and complies with real conditions.

Finite element modeling of reinforced concrete interior column-slab joints with and without shear reinforcement, as well as analysis of shear stress fields in the middle layer of the concrete plate were performed using STAAD.ProV8i. For proper calibration between the models, a definite finite solid model without shear reinforcement is analyzed and considered a reference sample. This study examines a new form of rigid shear reinforcement that eliminates steel congestion at joints and provides a simple approach to determining the rigid shear reinforcement arm.

Twelve slabs, 11 of which contained double-headed studs as shear reinforcement, were tested supported by central column and loaded concentrically. Their behavior is described in terms of deflections, rotations, strains of the concrete close to the column, strains of the flexural reinforcement across the slab width, and strains of the studs. All failures were by punching, in most cases within the shear reinforced region. The treatments of punching resistance in ACI 318, Eurocode 2 (EC2), and the critical shear crack theory (CSCT) are described, and their predictions are compared with the results of the present tests and 39 others from the literature. The accuracy of predictions improves from ACI 318 to EC2 to CSCT—that is, with increasing complexity. However, the CSCT assumptions about behavior are not well supported by the experimental observations.

Resumen: Las losas planas con vigas embebidas en estructuras de hormigón armado son ampliamente usadas en el Ecuador debido a su bajo costo, facilidad de construcción y aspecto arquitectónico. Las losas planas han demostrado que tienen un buen comportamiento ante cargas verticales, sin embargo, se han reportado numerosos colapsos estructurales en edificaciones con este sistema constructivo durante eventos sísmicos. El colapso producido en este tipo de estructuras es preocupante pues las fallas se han producido debido al punzonamiento de las losas alrededor de las columnas. Este tipo de falla ocurre de forma repentina y por lo tanto es necesario evitarla. No existe en el ACI la recomendación para el diseño de la conexión Losa – Columna, cuando se trata de pórticos sin muros o paredes estructurales. En este estudio, se construyeron dos modelos de prueba a escala real. Se construyeron 2 nudos interiores de un edificio con losas planas y fueron ensayadas ante una combinación de cargas verticales y laterales para observar el comportamiento de la conexión losa columna. La carga horizontal fue aplicada de forma cíclica y se colocó una sobre carga en la losa para simular la carga vertical de una edificación en servicio normal. Estos experimentos mostraron que el tipo de falla que se produce en estructuras de hormigón con losas planas es frágil. En ninguno de los dos modelos se produjo el agotamiento por flexión, sin embargo, sí se evidenciaron daños por corte en dos direcciones o punzonamiento.

Abstract: Flat slabs with hidden beams are widely used in reinforced concrete construction in Ecuador because of their low cost, short construction time and architectural appearance. Hidden beams are referred to beams that are as high as the flat slab. This kind of flat slabs has a good performance for vertical loads, however, several structural collapses have been reported during seismic events. These failures are commonly referred to as “punching shear” failures as the column appears to punch through the slab as the latter drops away from the failure surface around the column. These failures appear suddenly; therefore it is necessary to prevent them. In this experiment, two full scale specimens were constructed. Two interior slab - column connections were tested under gravity and seismic load to evaluate the slab column connection performance. The results showed that the failure of this structural system is fragile. In both specimens flexural yielding was not developed before the failure due to the punching shear.

This paper presents results of tests on 18 one-way reinforced concrete slabs under point loads having as main variable the transverse flexural reinforcement ratio, the loading position and the width of the slab. The response of the slabs is described and discussed in terms of deflections, strains of the concrete and of rebars, cracking pattern, failure modes and failure loads. Experimental results are also used to discuss and evaluate theoretical treatments presented by American Concrete Institute 318 (ACI, 2014) and Eurocode 2 (Comité Européen de Normalisation [CEN], 2005). All slabs failed by punching shear and results indicate that the recommendations presented by the codes are conservative, especially those related to the prediction of one-way shear resistance of reinforced concrete flat slabs. Resistência à punção de lajes de concreto armado com cargas concentradas assimétricas RESUMO. Este trabalho apresenta resultados de ensaios em 18 lajes unidirecionais de concreto armado sob carregamento concentrado, tendo como variáveis a taxa de armadura de flexão transversal, a posição de carregamento e a largura da laje. Seu comportamento é descrito e discutido em termos de deslocamentos, deformações do concreto e das armaduras, padrão de fissuração, modos e cargas de ruptura. Os resultados experimentais também são usados para discutir e avaliar as recomendações apresentados pelas normas ACI 318 (2014) e Eurocode 2 (CEN, 2005). Todas as lajes romperam por punção e os resultados indicam que as recomendações normativas são relativamente conservadoras, especialmente aquelas relacionadas com a previsão da resistência ao cisalhamento unidirecional de lajes lisas de concreto armado.

In this research, the punching shear behavior of high strength concrete bubble slab was investigated after burning in a real fire test until it reached 300 C° for 30 minutes and cooling gradually by air and rapidly by spraying water for (5 and 10) minutes of concrete by and quenching in water for 10 minutes. Experiment results show that using high strength concrete improves the cracking pattern, punching zone perimeter, angel of failure, and critical section of slabs due to improvements in the stiffness low er voids ratio in concrete microstructure and higher cement content but some drawbacks appear like higher spalling rate.

The standard design method (classical method) for reinforced concrete rectangular footings is: First, a dimension is proposed and should comply with the allowable stresses; subsequently, the effective depth is obtained from the maximum moment and is checked against the bending shear and the punching shear until, it complies with these conditions and, then, steel reinforcement is obtained, but it is not guarantee that the minimum cost will be obtained. This paper shows an optimal design for reinforced concrete rectangular footings using the new model. A numerical experimentation is presented to show the model capability to estimate the minimum cost design of the materials used for a rectangular footing that supports an axial load and moments in two directions in accordance to the
building code requirements for structural concrete and commentary (ACI 318-13). Also, a comparison is made between the optimal design and current design for rectangular footings. The solutions show that the optimal design is more economical and more precise with respect to the current design, because standard design is done by trial and error. Then, the optimal design should be used to obtain the minimum cost design for reinforced concrete rectangular footings.

This paper presents results of eight experimental tests carried to evaluate the mechanical performance of unconnected " W " stirrups. Reinforced concrete wide beams were tested and their characteristics were idealized to represent column strips in flat slab buildings. The main variables were: the type of shear reinforcement; the shear span to effective depth ratio (av/d); and the flexural (ρl) and shear (ρw) reinforcement ratios. In general, both the response and the shear resistance of the structural elements with unconnected " W " stirrups was similar to those elements with vertical closed stirrups. Increments of shear resistance of up to 84% were achieved, indicating that they have high potential for use as shear reinforcement in slab-column connections.

It is common practice to use a flat slab system not just in new construction buildings but also for adding extra stories like mezzanine floors for existing buildings. As such, non-monolithic connections are used, however, few literature either experimentally or numerically, addresses the behavior of such connections. In this respect, this paper numerically investigated the behavior of two non-monolithic connection (using dowel and weld systems) validated against experimental work conducted in the concrete laboratory of the Faculty of Engineering, Ain Shams University. In this context, a parametric investigation for the influencing parameters is presented. The investigated parameters were related to dowels number, diameter, impeded length inside the slab, the height difference between the dowels in X & Y directions, welding length, and slab thickness. The results illustrate the impact of the tested parameters on the performance of the proposed connections. This paper is considered a gate opening for a numerical database that facilitates the formulation of design equations for the proposed non-monolithic connection

Code design of slab-column connections to resist seismically induced drifts is currently based on empirical relationships for both moment and deformation capacity. The results of tests on slab-column connections are however sensitive to the conception of the test setup. This paper presents a new setup configuration as well as first results of an experimental campaign carried out at EPFL. Within this campaign slabs without shear reinforcement will be subjected to constant vertical loads and increasing seismic moments. Parameters investigated are the vertical loads, the longitudinal reinforcement content of the slabs, the column size and the loading history (monotonic vs. cyclic). Results of the first three out of sixteen tests showed that the drift capacity of relatively thick slabs is smaller when compared to thinner ones tested by other researchers [7]. The influence of the gravity induced shear force on the seismic moment and deformation capacity of the connections is found to be well pronounced. A comparison of a monotonic and cyclic test for high vertical loads showed that the deformation capacity of the cyclically loaded slab is smaller than of the monotonically loaded one.

The purpose of this experiment is to investigate the efficacy of including Glass fiber (polypropylene fiber) in enhancing the characteristics of concrete and punching shear strength of reinforced concrete bubble slabs exposed to elevated temperatures and water cooled. In this investigation, fifteen panels were tested. The models represent the negative bending moment zone surrounding an interior column supporting bubble slabs. One set of slab specimens was evaluated at room temperature, while the other three groups were examined with different cooling methods after being exposed to high temperatures. The test weights were increased incrementally until the maximum carrying capacity was reached. The following parameters were measured: Ultimate punching shear, deflections, crack patterns, angle of failure and critical zone.

Reinforced concrete (RC) flat slabs supported on columns are one of the most widely used structural systems for office and industrial buildings. In regions of medium to high seismic risk RC walls are typically added as lateral force resisting system and to increase the lateral stiffness and strength. Although slab-column systems are not expected to contribute to the lateral resistance of the structure due to their low stiffness, the slab-column connection have to have the capacity to follow the seismically induced lateral displacements of the building while maintaining the capacity to transfer the vertical loads from the slab to the columns. Otherwise, brittle punching failure of the slab occurs and the deformation capacity of the entire building is limited by the deformation capacity of the connection. The present paper presents a model for predicting the flexural behaviour of slab-column connections without transverse reinforcement when subjected to earthquake-induced deformations, considering both the load and the deformation of the slab. The model is based on the Critical Shear Crack Theory (CSCT) and presents a rational approach for predicting the transferred moment-rotation relationship of slab-column connections as well as the contribution of all resistance-providing mechanisms respecting equilibrium principles in both local and global level. The model proved to be accurate enough when compared with tests (monotonic and cyclic) found in the literature.