Research on Bearing Mechanism of Strut-and-Tie Model for Punching Failure of Independent Foundation Under Column

Through three-dimensional nonlinear finite element analysis, the punching failure’s bearing mechanism of the independent foundation under column whose slab is the size of 0.8m×0.8m×0.3m is obtained. The transfer mechanism of the foundation is spatial strut-and-tie model, where the reinforcements located in the link ranges between each adjacent corner of the slab are represented by ties, and the concrete distributed in the link ranges from the column bottom to four corners of the slab bottom are represented by struts. The indication of punching failure is that the concrete at the two ends of the struts reaches the shear-compression failure strength, and the punching cone is punched out relative to the slab, which has distinct punching failure features. A new spatial strut-and-tie model composed of four ties and four struts is proposed on the basis of clear bearing mechanism, which provides a new idea for the calculation of the punching bearing capacity of the independent foundation under column.

New insights into soil arching behaviour in column supported embankments

The observation of failure surfaces within column supported embankments is critical to understanding how the embankment stresses are transferred towards the column heads. In this study, finite element simulations utilising a strain softening constitutive model, non-local regularisation and the Arbitrary Lagrangian-Eulerian formulation are used to examine these failure surfaces over various embankment geometries. This methodology offers insights into the nature of the failure mechanism, the development of a plane of equal settlement and the influence of the subsoil settlement profile. Depending on the embankment geometry, the results indicate either a punching failure, inverted general bearing failure, or a localised failure develops. The transition between punching and inverted general bearing failure is found to be closely related to the establishment of a plane of equal settlement within the embankment. The height of the plane of equal settlement and the range of failure mechanisms that develop were largely insensitive to the nature of the subsoil settlement profiles simulated. These findings have implications for the practical design of efficient embankments and the effective design of future experimental studies.

NUMERICAL ANALYSIS OF LONGITUDINAL REINFORCEMENT EFFECT ON RC SLAB PUNCHING SHEAR RESISTANCE BY STRENGTH AND CRACK PROPAGATION CRITERIA

he article deals with the influnce of longitudinal reinforcement of the support zone of reinforced concrete slabs on the strength and crack resistance under the criterion for punching failure. The evaluation of impact was carried out by the method of numerical studies based on finite-elementcomputational technologies. The results of physical experiments published in the scientificliterature are taken as the basis for the conducted research. The existing provisions of the existing domestic and foreign standards for the calculation of slab reinforced concrete structures according to the criterion for punching failure are considered. The main provisions of the applied finit element approach are presented, verificationis performed and the correctness of the applied technique is justified In the numerical studies, the forecast of strength and crack resistance was done for considered reinforced concrete slab structures; the results of numerical studies were compared with the data from physical experiments and the evaluation results based on the relevant domestic and foreign regulations. According to numerical studies results it was stated that longitudinal reinforcement of the tensile zone of slab structure has a significantimpact on both the level of load-bearing capacity and the scheme of crack formation and propagation. The results of the implemented studies justify the necessity to revise the national standards of structural analysis for reinforcement concrete slab structures under the criterion for punching failure.

Field Static Load Tests of Post-Grouted Piles under Various Failure Conditions

In practice, inappropriate test set-up and design will result in pile eccentricity, reducing pile bearing capacity. Also, inappropriate piling will reduce the strength of the upper part of concrete. These pile elements under inappropriate design and construction are easy to be overlooked since they are invisible. Because the research focuses on the pile failure behaviour under different conditions, this paper aims to determine the outcomes of pile foundation under eccentric loading, pile with inadequate concrete strength, and pile with punching failure. Four concrete piles were cast, and compressive static load tests (SLTs) were performed. The top part of the first pile was cast with inadequate concrete strength. The other two piles were cast with achieved concrete strength; however, one of these applied with eccentric loading. The third pile was the standard pile, and the fourth pile was tested until punching failure occurred. For the fourth pile, the T-Z method was used for determining the failure characteristics. It is discovered that, for the pile with inadequate concrete strength, the cracks occurred at the pile head, and the concrete crushed at 0.9–1.2 m below the ground; for the pile suffering eccentricity, the partial concrete crushed, and the concrete from the opposite side suffered tension fracture; for the pile suffering punching failure, the crack on the soil extends up to 50 mm. Traditional result presentations and interpretations were also provided. Furthermore, it was found that, for the pile suffering punching failure, the shaft resistance increased as the loads increased, and after the loading achieved the maximum resistance, the loading transferred to the pile tip and finally led to the destruction of the pile-soil system.

Analysis and Experimental Study on Bearing Capacity of “All-Inclusive” Underpinning Joint

Aiming at the phenomenon of punching failure and large slip at the new-to-old concrete interface of “beam-column” underpinning joint, a new type of “all-inclusive” underpinning joint is tested and numerically analyzed, which adopts the spraying glue + grooving + planting bars + prestressed + hooping connection method. The experimental and numerical analysis results show that the connection method of “all-inclusive” underpinning joint can effectively avoid punching failure of the joint, and the failure mode is mainly flexure-shear. Then, the “all-inclusive” underpinning joint can delay the initial slip at the new-to-old concrete interface and reduce the overall slip. Finally, combining the theoretical and experimental results, a simplified calculation formula for the bearing capacity of the “all-inclusive” underpinning joint is improved. The theoretical results are in good agreement with the experimental results, which indicates that the calculation of the bearing capacity of the underpinning joint using the formula in this paper is feasible and can provide experimental and theoretical references for similar projects.

Tests of Slab-Column Connections Subjected to Reversed Cyclic Moments in Addition to Different Levels of Gravity Shear Load

Reinforced concrete flat slab-column structures are widely used because of their practicality. However, this type of structures can be subjected to punching-shear failure within the slab-column connections. Without shear reinforcement, the slab-column connection can undergo brittle punching failure, especially when the structure is subjected to lateral loading in seismic zones. This research is a part of an extensive investigation about the punching shear behaviour of interior RC slab-column connections under seismic loading. The main objective is to discuss the effect of the gravity shear level on the punching shear behaviour[1].The current paper represents only the results of the first four tested specimens without shear reinforcement. The first specimen was tested subjected to vertical gravity load only without cyclic loading while the other three specimens were tested under different vertical loads V which was kept constant during testing in addition to a reversed displacement controlled cyclic loading which was increased up to punching shear failure. The gravity load V was chosen as 0.4, 0.6 and 0.8 V0 respectively, where V0 is the vertical load causing punching shear failure according to ACI318-14[2]. All tested specimens have the same slab dimensions of 2000x2000mm, slab thickness 200mm, flexural reinforcement ratio of 1.62% and the same column dimensions 250mm x 250mm. Finally, the experimental results are analyzed and compared to international codes such as American Code ACI318-14 and Euro Code EC2-2004[3]. In light of these results, some preliminary conclusions are presented.

Modelling and analysis the effect of unbalanced moment directions on behaviour of edge column-slab connections

This research investigates the effect of unbalanced moment directions on the behaviour of edge column slab connections using a finite element analysis. The analyses were done on subassembly edge column slab connections that were designed according to Indonesian Concrete Standard (SNI 2847:2013). Three unbalanced moment directions were considered namely perpendicular, parallel and inclined 45° to the slab free edge. The concrete damage plasticity (CDP) and truss elements in Abaqus were utilized to model and analyse the behaviour of concrete and reinforcement bars, respectively. The modelling techniques were first validated using an experimental result available in the literature. There are five parameters in the CDP model need to be validated to get convergent results with the experimental data. Using the CDP validated parameters, then seven specimen models were analysed under combined shear force and an unbalanced moment in three directions. The ratio of M/V was kept constant of 0.3. The results show that the punching failure capacity of connections having an unbalanced moment inclined 45° is smaller than that of an unbalanced moment perpendicular to the slab free edge, but higher than that of an unbalanced moment parallel to the slab free edge. The patterns of concrete strain are consistent with the moment directions. All tension rebars passing through column sections yield at the connection failures.

The Maximum Punching Capacity of Flat Slabs

Two ways how to determine maximum punching resistance of flat slabs with shear reinforcement are currently used. The first way is verification of the concrete strut capacity at the column periphery defined as VRd,max. The second limit is defined as kmax multiple of the punching shear resistance without shear reinforcement VRd,c. The values of kmax are proposed usually in between 1.4 and 2.0. Results of the experimental tests are presented in the paper that were focused on above mentioned limits, whether failure of the struts can precede any other form of punching failure that is limited by kmax*VRd,c. Two experimental slab samples reinforced with high amount of shear reinforcement that increased punching capacity above capacity of the concrete struts were tested together with two slab samples cast without shear reinforcement. Comparison has shown that punching resistance of flat slab with shear reinforcement has been 1.7 times higher than resistance without shear reinforcement. While some standards allow for use kmax value of 1.9 in this case. This indicates that limits based only on the kmax factors may overestimate actual maximum punching shear resistance.