ISSN: 0090-3973
Page Count: 8

ISSN: 0090-3973
Page Count: 8

ISSN: 0090-3973
Page Count: 8

Qualitative Assessment of Failure in Bolted Connections: Maximum Stress Criterion
Anabtawi, MZ
University of Bahrain,

Nazzal, JM
Natural Resources Authority,

Pascual, FG
Assistant professor, St. Cloud State University, MN

Meeker, WQ
Professor, Iowa State University, IA

Patton-Mallory, M
Assistant director, USDA Forest Service, CO

Pellicane, PJ
Professor of wood engineering, Colorado State University, CO

Smith, FW

Patton-Mallory, M
Assistant director, USDA Forest Service, CO

Pellicane, PJ
Professor of wood engineering, Colorado State University, CO

Smith, FW

James, MR
Member Technical Staff, Rockwell International Science Center, Calif.

Morris, WL

Abstract

A geochemical analysis of El-lajjun oil shale in Jordan was carried out. It was found that El-lajjun oil shale consists of the following groups: organic matter, biogenic calcite and apatite, detrital clay minerals, and quartz. The calorific values of 100 samples of shale were determined. The effect of bore depth, calcium carbonate, organic carbon, and sulfur content on the calorific values were studied. Results were well correlated by the following equation Calorificvalue=352,44Caret(CaCO3)-0.066(S)0.257(Corg)1.141 with correlation coefficient of 0.983 and with an average standard error of 2.63%.

We present modified sudden death test (MSDT) plans to address the problem of limited testing positions in life tests. A single MSDT involves testing k specimens simultaneously until the rth failure. The traditional sudden death test (SDT) is a special case when r=1. The complete MSDT plan consists of g single MSDTs run in sequence. When r>1, there can be up to r−1 idle test positions at any time. We propose testing “standby” specimens in the idle positions and use simulation to gage the improvement over the basic MSDT plan. We evaluate test plans with respect to the asymptotic variance of maximum likelihood estimators of quantities of interest, total experiment duration, and sample size. In contrast to traditional experimental plans, shorter total testing time and smaller sample sizes are possible under MSDT plans.

This paper presents information regarding the distribution of critical stresses and regions where failure is likely to initiate in single bolt wood connections loaded in tension. Predicted stresses are the results of a three-dimensional numerical analysis of a connection consisting of a single steel pin and a wood member with a hole. Stresses of particular interest are: parallel-to-grain compression and shear and perpendicular-to-grain tension. Failure location is determined by considering the regions of the member where the material capacity is exceeded in at least one of the three aforementioned stresses. No stress interaction is assumed in this analysis.

A recently developed and verified three-dimensional (3-D) finite element model was used in this study. Important features of this model include a trilinear constitutive model of the nonlinear behavior of wood and a mechanism to describe the contact between the pin and the hole with changing connection load. The connection geometries studied included a single ratio of end distance to pin diameter (e∕d=4) and three bolt aspect ratios (length of bolt in wood member/bolt diameter) (l∕d=2,5,and7).

Stress contours are illustrated on the 3-D wood member surface, on the contact surface, and on planes of symmetry. Pin and wood deformations are also illustrated.

The results show that for connections with an (l∕d)=2, stresses are nearly uniform through the wood member thickness with negligible pin yielding. For connections with the larger bolt aspect ratios, considerably more pin bending and yielding is predicted with nonuniform stress distributions through the member thickness. The maximum stress failure criterion is found to be useful for comparing numerically predicted stress distributions to failure modes observed experimentally. By making these comparisons, it is possible to make qualitative interpretations of the critical stress states to indicate the regions where failure is likely to occur.

In a companion paper, a characterization is presented of stress fields in a single-shear bolted connection subjected to tension loading. Numerous stress contours are presented that illustrate the magnitude of the parallel-to-grain compression and shear stresses, as well as the perpendicular-to-grain tension stresses. In addition, regions of potential failure in the selected specimens are identified based on a maximum stress failure criterion.

The work presented in this paper represents additional efforts to identify the effect of stress interactions on the strength of the previously mentioned connections. The Tsai-Wu criterion, quantified by its failure index, is used as the tool to identify stress interactions between the aforementioned stress components. Connection geometries similar to those discussed in the companion paper [end distance/bolt diameter (e∕d)=4; and length of bolt in main member/bolt diameter (aspect ratio) (l∕d)=2,5,and7] are studied. In addition, several other geometries are discussed that illustrate the effects of changing aspect ratio and end distance.

A number of significant findings are reached in this study. As is the case in the companion study, all connections with (l∕d)=2 have nearly uniform distributions of the Tsai-Wu failure index (FI) through the specimen thickness. No significant pin bending is associated with this geometry. Connections with l∕d>4 have a failure mode (interpreted from the numerical model) that includes substantial pin bending due to steel yielding, wood crushing, and localized cracking.

Keywords:
bolted connection, wood, finite element model, maximum stress failure criterion

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