Simplified Pushover Analysis for Rapid Assessment of Shear-Type Frames

A simplified pushover method for rapidly assessing the seismic capacity of shear-type frames is presented. The frame global force-displacement capacity is described as a trilinear curve passing through three limit states (LS): Damage LS (DLS), Life safety LS (LLS), and Collapse LS (CLS). The global LSs are obtained consequently to the attainment of story-level, element-level, and section-level LSs. All LS capacities are described through closed-form equations. The validity of the proposed method is verified by applying it on several reinforced concrete (RC) frames with a varying number of stories. The results obtained with such an analytical procedure show a good match with those obtained from pushover based on finite element method (FEM) analysis models, in terms of both global force-displacement capacity curves and story displacements at various LSs. The proposed method has the potential to be conveniently applied in large-scale vulnerability/risk assessment studies, where the quality and quantity of the available data call for the use of simplified yet accurate models. More refined models would in fact require significantly heavier computational efforts, not justified by the quality of the results that are usually obtained. The simplicity of the proposed method in such a context is demonstrated through the development of the fragility curves of a five-story shear-type reinforced concrete frame, starting from a predefined set of mechanical and geometrical features characterizing a building typology.

Experimental Study on Formation Slip under Injection-Production Interregional Pressure Difference Based on the Abnormal Similarity Theory

In oilfield development, the pore pressure difference between adjacent areas leads to cracks and slipping in the weak structural surface layer, which triggers the shear failure of the casing. The formation slip involves a large range of formation, and its amount is not proportional to the size of the slipping rock mass, which conventional physical models cannot simulate. In this study, based on the abnormal similarity theory, we derived the similarity coefficients of mechanical parameters with different horizontal and vertical proportions. Furthermore, an experimental device for simulating the formation crack and slip under interregional formation pressure difference was developed. Through the experiments, we obtained slip conditions under different pressure differences between adjacent areas and different oil layers and fault surface depths. The study shows that the pore pressure difference between adjacent areas is the driving force of the formation slips. The slip zone is located in the middle of two abnormal pressure zones, and the distance between the adjacent areas can affect the slip range. The deep burial of the oil layer and shallow depth of the weak structural surface can trigger a more significant formation slip. The experimental method proposed in this paper provides an experimental device and method for understanding the formation of cracks and slips on weak structural surfaces. The experimental results provide a theoretical basis for the prevention of shear-type casing damage caused by formation slip.

In-plane compression modulus and strength of Nomex honeycomb cores

The stress-strain response and deformation mechanism of a range of Nomex honeycomb cores tested under in-plane compression has been examined experimentally. The cores with a thin wall displayed extensive bending deformation of the cell walls inclined to the horizontal (loading is vertical) and failed in bending. The cores with thicker walls failed by a shear-type instability of the cells indicated by tilting of vertical cell wall segments. The failure strain decreased with increasing core density. The modulus and compressive strength of the core were compared to micromechanical predictions. Normalized modulus and strength values varied between the various cores. The average modulus and strength results allow backing out of the modulus and bending strength of the Nomex paper. The results were in reasonable agreement with published tensile test results and composite micromechanics.

Identification of Structural Parameters Based on HHT and NExT

Signal processing approaches are widely used in the field of earthquake engineering, especially in the identification of structural modal parameters. Hilbert-Huang Transformation (HHT) is one new signal processing approach, which can be used to identify the modal frequency, damping ratio, mode shape, even the interlayer stiffness of the shear-type structure, incorporating with Natural Excitation Technique (NExT) method to take information from the response records of the structure. The stiffness of the structure is of great importance to judge the loss of its bearing capacity after earthquake. However, all of modal parameters are required to calculate the stiffness of the structure by use of HHT and NExT, which means that the response records shall contain all of modal information. However, it has been found that the responses of the structure recorded only contain the former order modal information; even it is excited by earthquake. Therefore, it is necessary to found a formula (formulas) to calculate the stiffness only using limited modal parameters. In this paper, the calculation formulas of the interlayer stiffness of shear-type structure are derived by using of the flexibility method, which indicate that all of interlayer stiffnesses could be worked out as long as any one set of modal parameters is obtained. After that, Taking Sheraton-Universal Hotel subjected to North Bridge earthquake in 1994 as an example, HHT and NExT are used to identify its modal parameters, the derived formulas are used to calculate the interlayer stiffnesses, and their applicability and accuracy are verified.

LATERAL HUMERAL CONDYLAR FRACTURE IN A PAEDIATRIC MONTEGGIA TYPE III EQUIVALENT

Monteggia fracture dislocations can be classic or equivalents. Equivalents, also known as Monteggia like lesions, are very rare especially type III and IV, which have been added to the literature after Luis Bado presented the original classification system of Monteggia fracture dislocations. Type III equivalent is classically defined as a proximal ulna fracture associated with a fracture of the lateral condyle of the humerus. In the literature only seven such cases have been reported so far. Here we present two such cases where one eight-year-old boy had a complex type of injury with a shear type fracture of the lateral humeral condyle and other a seven-year-old boy who had a plastic deformity of the ulna with an avulsion type fracture of the lateral humeral condyle. We also try to describe a novel mechanism of injury, known as, “Barzulla circle”, for the classical as well as equivalent type III Monteggia fracture dislocations.

A Nonlinear Cable Bracing Inerter System for Vibration Control

This study proposes a nonlinear cable model for the cable-bracing inerter system (CBIS). In a CBIS, cables are introduced to connect inerter systems and the structure for translation-to-rotation conversion. This CBIS employs an inerter element, a nonlinear cable bracing element and an additional damping element to utilize their synergy benefits. This paper aims to investigate the control effect of the nonlinear CBIS for high-rise buildings that are represented as bending-shear type models. First, a nonlinear inerter system is incorporated into a single-degree-of-freedom (SDOF) system and the mechanical model is proposed. An optimum design method is then developed for a high-rise building system equipped with a CBIS and the time-history analyses are conducted to validate the control effect of the CBIS. It is concluded that the employment of a CBIS can substantially improve the structural performance. A genetic algorithm can be used to obtain optimal parameters of a CBIS, thereby more effectively reducing the dynamic response of high-rise buildings.

Modelling of Reversed Austenite Formation and its Effect on Performance of Stainless Steel Components

The kinetics of reversed austenite formation in 301 stainless steel and its effect on the deformation of an automobile front bumper beam are studied by using modelling approaches at different length scales. The diffusion-controlled reversed austenite formation is studied by using the JMAK model, based on the experimental data. The model can be used to predict the volume fraction of reversed austenite in a temperature range of 650 - 750 C. A 3D elastoplastic phase-field model is used to study the diffusionless shear-type reversed austenite formation in 301 steel at 760 C. The phase-field simulations show that reversion initiates at martensite lath boundaries and proceeds inwards of laths due to the high driving force at such high temperature. The effect of reversed austenite (RA) on the deformation of a bumper beam subjected to front and side impacts is studied by using finite element (FE) analysis. The FE simulations show that the presence of reversed austenite increased the critical speed at which the beam yielded and failed. RA fraction also affects the performance of the bumper beam.