Raphael Grzebieta

Concrete-filled circular steel tubes subjected to pure bending

Current design codes and standards provide little information on the flextural behaviour of circular concrete filled tubes (CFT) as there have been few experimental studies. There are significant differences in d/t-limits recommended in various codes for CFT under bending. This paper presents an experimental investigation of the flexural behaviour of circular CFT subjected to large deformation pure bending where d/t = 12 to 110. The paper compares the behaviour of empty and void-filled, cold-formed circular hollow sections under pure plastic bending. It was found that for the range of d/t40, void filling prevented local buckling for very large rotations, whereas multiple plastic ripples formed in the inelastic range for specimens with 74d/t110. In general, void filling of the steel tube enhances strength, ductility and energy absorption especially for thinner sections. Based on the measured material properties, the plastic d/t-limit was found to be 112. A simplified formula is provided to determine the ultimate flexural capacity of CFT. The existing design rules for the ultimate moment capacity of CFT may be extended conservatively to a new slenderness range of 100ls 188. uf6d9 2001 Elsevier Science Ltd. All rights reserved.

Tests on concrete filled double-skin (CHS outer and SHS inner) composite short columns under axial compression

This paper presents stub columns tests on concrete-filled double skin sandwich tubes (CFDT) constructed using cold-formed steel tubes. The annulus is filled with micro high-strength concrete having compressive cylinder strength of 64 MPa. The outer skin is made of circular hollow sections (CHS), while the inner skin is made of square hollow sections (SHS). Eight different section sizes were used for the outer skin with diameter-to-thickness ratio ranging from 19 to 55. Three section sizes were chosen for the inner skin with width-to-thickness ratio in the range of 20 to 26. The CFDT construction was found to have significant increase in strength, ductility and energy absorption over the outer jacket. A simplified formula is derived to determine the compressive capacity of CFDT and compared against the current design rules. The proposed formula was found in good agreement with experimental results. This paper also verifies the yield slenderness limit (λey) of 82 specified in AS 4100 for cold-formed CHS stub columns.

Plastic mechanism analysis of circular tubes under pure bending

Abstract There are a number of solutions available to predict the response of a circular steel tube under pure bending. However, most of these solutions are based on an elasto-plastic treatment, which is complex and difficult to use in any routine design. This paper describes a theoretical treatment to predict the moment-rotation response of circular hollow steel tubes of varying D / t ratios under pure bending. The Mamalis et al. (J. Mech. Sci. 1989;203:411–7) kinematics model for a circular tube under a controlled moment gradient was modified to include the effect of ovalisation along the length of the tube. Inextensional deformation and rigid plastic material behaviour were assumed in the derivation of the deformation energy. The plasticity observed in the tests was assumed to spread linearly along the length of the tube. Two local plastic mechanisms (Star and Diamond shapes) were studied to model the behaviour observed in the tests especially during the unloading stage. The theoretical predictions are compared with the experimental results recently obtained by Elchalakani et al. (Quartral. J. Struct. Eng. 2000;3(3):1–16). Good agreement was found between the theoretical predictions and experimental moment-rotation responses, particularly for the Star shape mechanism. A closed-form solution is presented suitable for spreadsheet programming commonly used in routine design.

Bending tests to determine slenderness limits for cold-formed circular hollow sections

There are significant differences in slenderness limits recommended in various codes for circular hollow sections (CHS) under bending as there have been little experimental studies. In this paper an attempt is made to establish more accurate slenderness limits for cold-formed circular hollow sections. This paper describes a series of bending tests to examine the influence of section slenderness on the inelastic bending properties of cold-formed CHS. Twelve bending tests were performed up to failure on different sizes of CHS with diameter-to-thickness ratio d/t ranging from 37 to 122. This range of d/t was obtained by machining as-received coldformed circular hollow sections grade C350L0. The test results are compared with other experimental data and the design rules given in various steel specifications. The slenderness limits were established to define Class 1 (compact), 2, 3 (non-compact) and 4 (slender). These limits were based on modifications of criteria for rotation capacity commonly used for steel structures. A design curve was developed and recommended for the design of cold-formed CHS under pure bending. uf6d9 2002 Elsevier Science Ltd. All rights reserved.

Development of a multidisciplinary method to determine risk factors for arm fracture in falls from playground equipment

Objectives: To present the development of a novel multidisciplinary method to investigate physical risk factors for playground related arm fracture. Rationale: Previous playground injury research has been limited in its ability to determine risk factors for arm fractures, despite their common and costly occurrence. Biomechanical studies have focused exclusively on head injury. Few epidemiological studies have quantified surface impact attenuation and none have investigated specific injury outcomes such as arm fracture. Design: An unmatched case-control study design was developed. An instrumented child dummy and rig were designed to simulate real playground falls in situ. Validated output from the dummy was used to quantify arm load. Other field measurements included equipment height, fall height, surface depth, headform deceleration, and head injury criterion. Discussion: Validated methods of biomechanics and epidemiology were combined in a robust design. The principle strength of this method was the use of a multidisciplinary approach to identify and quantify risk and protective factors for arm fracture in falls from playground equipment. Application of this method will enable countermeasures for prevention of playground related arm fracture to be developed.

Plastic Collapse Analysis of Slender Circular Tubes Subjected to Large Deformation Pure Bending

This paper presents a plastic mechanism analysis for thin-walled circular hollow section (CHS) tubes deforming in a multi-lobe or diamond collapse mode under large deformation pure bending. The fold formation process was such that the shell curvature flattened on the compression side transforming into a definite number of flat triangles attached to each other. The collapse proceeded progressively by folding about the base and sides of these triangular planes and over traveling hinge lines. The collapse mechanism was similar to the diamond crush mode. An existing kinematic model for an axially compressed thin-walled circular tube was modified to predict the collapse curve of a thin-walled tube under bending. Inextensional deformation and rigid plastic material behaviour were assumed in the derivation of the deformation energy. Ovalisation was observed during the test and its deformation energy was determined and found significant. An expression for the plastic collapse moment was obtained by equating the total energy absorbed in bending, rolling and ovalisation to the external work carried out during a given cycle of deformation. Comparisons of the predicted post-buckling moments and slopes of the collapse curves with those obtained from experiments carried out by the authors on cold-formed circular hollow sections show very good agreement.

Buckling of wide struts/plates resting on isotropic foundations

Abstract Starting from an Airy stress function in plane strain a new solution is presented for the buckling of plates on elastic foundations with in-plane loading. Saint Venants Principle is shown to play an important part in plate buckling behaviour when ‘deep’ foundations are present. Results are compared with those from Winklers and Pasternaks models and they demostrate that, provided certain restrictions are satisfied, the latter can give reasonably accurate results.

Response of Far-Side Occupants in Car-to-Car Impacts with Standard and Modified Restraint Systems using Hybrid III and US-SID

This paper provides a summary of preliminary results of three car-to-car 90-deg (1.6-rad) lateral impact crash tests with initially restrained Hybrid III and Side Impact Dummy (US-SID) dummies. These tests comprised part of a collaborative research project between Monash University, Autoliv Australia, and the Royal Automobile Club of Victoria. The overall research project objectives were to investigate the nature of nonstruck-side occupant injuries in automobile side impacts and to develop technical solutions to reduce these injuries. The test program results showed that a sash belt with a pretensioner and good geometry was effective in reducing occupant lateral excursions and lap belt loads. An increase in occupant neck loading was, however, observed and measured. Lateral torso seat restraints helped to prevent direct contacts between adjacent occupants resulting in a reduced head injury criterion (HIC) measured for a nonstruck-side occupant dummy.

PA 15-6-2811 Anatomical and biomechanical considerations for shunting-type hip protector function

Hip fracture remains a major cause of death and disability among older persons. Anatomical and biomechanical design considerations for shunting-type hip-protectors were investigated to address low user compliance among older-persons. Aims were to assess the hip muscle morphology as a load-attenuating medium during shunting: determine the material properties of skeletal muscle; and assess shunting-type hip-protector function in lateral falls. Low and high hip fracture risk groups were identified based on BMI. A three dimensional map was developed to measure muscle thickness at 15 points and volume (of gluteal and quadriceps) using CT. A new method was developed to measure material properties of skeletal muscle under fall conditions by impacting muscles in the in-situ state, substituting ovine for human specimens. Biomechanical kinematic data, the effect of specimen size and impact velocity were also analysed. Finite element simulations were then conducted to evaluate hip-protector function. Significant differences in muscle thickness were revealed between hip fracture risk groups. The strong relationship of muscle thickness to subjects’ body mass allowed development of mathematical models that estimate the maximum muscle thickness and muscle thickness based on location, both from subject mass. An average 17% increase in muscle volume was quantified for an equivalent 10u2009kg increase in subject mass. Males exhibited 3%–23% increased volume over females depending on the muscle. Material properties of skeletal muscle revealed an average Young’s Modulus of 0.06u2009MPa. Fall simulations quantified peak loads shunted to the iliac bone, greater trochanter and femoral shaft. Findings Suggest reducing protector size for greater wearer acceptance may cause injury elsewhere, especially for lean individuals at high fracture risk. Rather, hip-protector design should be based more on individual body constitution to increase effectiveness and comfort, and therefore user compliance. Muscle size should be maintained to allow effective use of preventive strategies within normal anatomical limits.