Finite Element Analysis of Structural Behavior of Sliding-Type Blast-Resistant Doors Based on Blast Loading Conditions

In current specifications, it is assumed that the structural performance is the same if the same deflection occurs, regardless of the structural characteristics or explosive conditions. However, depending on the structural characteristics and explosion conditions, structural responses may differ. Therefore, flexural deflection and shear need to be considered. In this study, the differences in the structural behaviors of steel-concrete sliding-type blast doors in the impulsive, dynamic, and quasi-static regions were analyzed using the finite element method. The results showed that in the impulsive region and under significant impact forces, shear failure occurred at the initial behavioral step, and the door was more vulnerable to shear than in the dynamic and quasi-static regions. Furthermore, in the impulsive region, a relatively large deformation occurred in the wheel installed on the lower part of the door, affecting functionality, such as opening and closing. Because combined flexural-shear and direct shear failures cause more damage than flexural failure, they must be considered during the design process, and further studies are required to develop a generalized evaluation method and design criteria to reflect the shear effect.

Torsion-shear behaviour at the interfaces of rigid interlocking blocks in masonry assemblages: experimental investigation and analytical approaches

Increasing interest has recently been devoted to interlocking blocks/interfaces capable to enhance the sliding resistance of masonry joints to external forces. In this framework, this paper deals with the assessment of the torsion-shear capacity of the contact interface between the lock and the main body of an interlocking block, assumed to have a cohesive behaviour. The interlocking block is a rigid unit which, on its faces, have square cuboidal locks keeping the adjacent/overlapped blocks together and preventing blocks from sliding. Two numerical approaches and a novel ad hoc experimental investigation are proposed to simulate the torsion-shear behaviour by applying eccentrical shear forces to the lock. First, concave, convex and corrected concave formulations provided by the literature for assemblages of rigid blocks with conventional planar joints are extended to model the interlocking block behaviour. Then, according to a second approach based on the discrete element method, the concave-shaped interlocking block is modelled by convex polyhedrons representing the lock and the main body of the block, considered as individual rigid units stacked over each other with a cohesive contact in between. A novel experimental investigation on the limiting pure shear and torsion-shear combinations at the lock interface made of cohesive material is also presented. Two different mortars were chosen to make the specimens, which were casted using 3D printed moulds, and different test configurations were set up to simulate shear and torsion-shear failures. The analytical and numerical results are compared with each other and against the experimental ones, with interesting remarks on the application of the different approaches.

Torsion-shear behaviour at the interfaces of rigid interlocking blocks in masonry assemblages. Experimental investigation and analytical approaches

Increasing interest has recently been devoted to interlocking blocks/interfaces capable to enhance the sliding resistance of masonry joints to external forces. In this framework, this paper deals with the assessment of the torsion-shear capacity of the contact interface between the lock and the main body of an interlocking block, assumed to have a cohesive behaviour. The interlocking block is a rigid unit which, on its faces, have locks keeping the adjacent/overlapped blocks together and preventing blocks from sliding. Two numerical approaches and a novel ad hoc experimental investigation are proposed to simulate the torsion-shear behaviour by applying eccentrical shear forces to the lock. First, concave, convex and corrected concave formulations provided by the literature for assemblages of rigid blocks with conventional planar joints are extended to model the interlocking block behaviour. Then, according to a second approach based on the discrete element method, the concave-shaped interlocking block is modelled by convex polyhedrons representing the lock and the main body of the block, considered as individual rigid units stacked over each other with a cohesive contact in between. A novel experimental investigation on the limiting pure shear and torsion-shear combinations at the lock interface made of cohesive material is also presented. Two different mortars were chosen to make the specimens, which were casted using 3D printed moulds, and different test configurations were set up to simulate shear and torsion-shear failures. The analytical and numerical results are compared with each other and against the experimental ones, with interesting remarks on the application of the different approaches.

Analysis of Raised Feature Failures on 3D Printed Injection Moulds

Background: Polymer-based 3D Printed Injection Mould (3DIM) inserts are used as a cost-effective method for low volume injection moulding (50–500 parts). However, abrupt failure leading to a short tool life is a common shortcoming of 3DIM. Need: The underlying causes of raised feature failures on 3DIM are not well known. Failure is commonly attributed to bending or shearing of raised features on the tool. Understanding the causes may help in delaying the failure and increasing tool life. Approach: Tool failure was analysed from a first-principles perspective, using pressure and temperature fields as determined by mould flow simulation. Experimental results were also obtained for two types of tool material (Visijet M3-X and Digital ABS) with polycarbonate (Lexan 943A) as the part material. Findings: Results find against the idea that pin failure in 3DIM tools is caused by bending and shear failures induced by injection pressures. We also conclude that failure of raised features is not necessarily an abrupt failure as mentioned in the literature. Originality: The generally accepted explanation for the failure of raised features in 3DIM tooling is that injection pressures cause bending and shear failure. This paper disconfirms this notion on theoretical and experimental grounds.

Mesoscale Modelling of Concretes Subjected to Triaxial Loadings: Mechanical Properties and Fracture Behaviour

The mechanical properties and fracture behaviour of concretes under different triaxial stress states were investigated based on a 3D mesoscale model. The quasistatic triaxial loadings, namely, compression–compression–compression (C–C–C), compression–tension–tension (C–T–T) and compression–compression–tension (C–C–T), were simulated using an implicit solver. The mesoscopic modelling with good robustness gave reliable and detailed damage evolution processes under different triaxial stress states. The lateral tensile stress significantly influenced the multiaxial mechanical behaviour of the concretes, accelerating the concrete failure. With low lateral pressures or tensile stress, axial cleavage was the main failure mode of the specimens. Furthermore, the concretes presented shear failures under medium lateral pressures. The concretes experienced a transition from brittle fracture to plastic failure under high lateral pressures. The Ottosen parameters were modified by the gradient descent method and then the failure criterion of the concretes in the principal stress space was given. The failure criterion could describe the strength characteristics of concrete materials well by being fitted with experimental data under different triaxial stress states.

Flexural and Shear Behavior of Beams Reinforced with GFRP Rebars

A new inexperienced constructing material is glass fibre reinforced polymer (GFRP) rebar. GFRP rebars are noncorrosive, non-conductive, light-weight substances and have an excessive longitudinal tensile capacity that is beneficial for use in civil infrastructure applications. In this analysis, the overall performance of GFRP rebar-reinforced concrete beams was assessed. Full scale exams had been conducted underneath fourpoint bending on eight one hundred fifty x 250 x 1500 mm beams to inspect the influence of GFRP specimens reinforced through both GFRP or metal rebars with flexural reinforcement ratios (ρf ) ranging from 0.53 to 1.45 times the balanced ratio (ρfb). In phrases of crack pattern, load deflection behaviour, load strain conduct and peak capacity, the check facts used to be analysed to decide the flexure and shear conduct of GFRP RC beams. The find out about confirmed that the ultimate load capacity of beams is immediately proportional to the flexural reinforcement ratio, and for steel bolstered specimens, cracking moments had been greater, relative to GFRP. For GFRP RC beams, the peak carrying ability is extra than steel beams. GFRP beams confirmed greater deflections than bolstered beams of steel. The findings additionally confirmed that the building of GFRP bolstered beams in concrete with GFRP stirrups can be influenced by means of shear failures. The reinforcement ratio and shear design of GFRP bolstered concrete beams is affected by way of their behaviour.

Response of an Existing Two-Storey RC Frame Designed for Gravity Loads: In Situ Pushover Tests and Numerical Analyses

The purpose of the research was to study the response of existing constructions, designed for gravity loads only in the South of Italy, more precisely in the Sicily Region. The building is an existing two-story reinforced concrete structure, built in the ‘80s. In order to design the test, numerical study on the structure has been conducted, using information reported on original design drawings or derived by in situ geometric and material investigation. A number of numerical models and pushover analyses of the structure have been carried out, in order to account for the uncertainties related to possible different responses. The numerical analyses aimed at estimating the capacity of the structure in terms of both force and displacement, the ductility reserve, and the most likely sequence of formation of plastic hinges. The pseudo-static cyclic test was designed to push and pull the building in one direction at increasing displacement levels, up to a drift of about 2%. At the end of the test, the infill panels were completely collapsed. Beams, columns, and joints showed plastic hinges and shear failures in different parts of the structure, with spread spalling of the concrete. Numerical and experimental results were found in fair agreement.

Design analysis of end notch flexure sandwich specimen with honeycomb core

Laminate beam theory based design analysis of the sandwich End Notch Flexure (ENF) test specimen is presented. The analysis is specifically considering specimens with honeycomb core, prone to in-plane compression failure of the core, other undesirable failure modes such as face indentation and core shear failure are analyzed. In addition, crack stability and energy dissipation due to frictional sliding between the crack surfaces are analyzed. Parametric analysis of ENF specimens with a range of face and core thickness, is presented to guide the design. In-plane compression failure of the core, but shorten the range of crack lengths were stable growth occurs. A thicker face will also increase the critical load for crack propagation and by so elevate the risk for indentation and core shear failures. Increased core density is beneficial for preventing indentation and core shear failures, but may increase the risk for in-plane compression failure of the core. The thickness of the core does not strongly influence the critical load for crack propagation. A thicker core increases frictional energy loss, but reduces the risk for core shear failure. A thicker core, however, makes the ENF specimen more prone to in-plane compression failure. ENF sandwich specimens with foam and honeycomb core were tested. The test results support the design analysis.