Stiffener Design for Beam-to-Column Connections Michelle L. Holland Thesis submitted to the Faculty of the Virginia Polytechnic Institute and State University in partial fulfillment of the requirements for the degree of Master of Science in Civil Engineering Dr. Thomas M. Murray, chair Dr. W. Samuel Easterling Dr. Siegfried M. Holzer September 1999 Blacksburg, Virginia Keywords: Moment Connections, Stiffener Design, Column Stiffeners Copyright 1999, Michelle L. Holland
Stiffener Design for Beam-to-Column Connections Michelle L. Holland (ABSTRACT) Stiffeners are used as a means of providing additional support to columns at beam connection locations. They are added when the strength of the column is exceeded but full moment strength of the beam section is desired. In determining the design of column stiffeners, there are no specifications for determining the distribution of load between the column web and stiffeners. The AISC Load and Resistance Factor Design Specifications provides guidelines for determining the stiffener area but no specifications are given. The actual loads taken by the stiffener and web are therefore not truly known. In this study, experiments were done to determine the load supported by the stiffeners and web when tensile forces are applied to the specimen. The initial stiffener design for the test specimens was based on LRFD guidelines. The actual load distribution between the column web and stiffeners is determined from strain data obtained during testing. This distribution is compared with the assumed loads obtained from the initial LRFD calculations. Finite element analysis is also utilized to confirm the consistency of the results obtained from the experiments. Using this information, a new method is developed which better predicts the distribution of load between the column web and the stiffener.
ACKNOWLEDGMENTS I owe a great deal of thanks to my family and friends who have always offered their support and belief in me. I could not have made all the accomplishments throughout my life without them. Dr. Thomas M. Murray has also provided guidance and has challenged me during my graduate studies. For this, and for his patience, I extend my greatest thanks. I also extend my thanks to Dr. W. Samuel Easterling and Dr. Siegfried M. Holzer for their help, knowledge, and participation as members of my committee. To Dennis Huffman and Brett Farmer, I also offer my appreciation for their help the Structures Laboratory and for the hours of enjoyment. iii
TABLE OF CONTENTS ABSTRACT ii ACKNOWLEDGMENTS iii TABLE OF CONTENTS iv LIST OF FIGURES vi LIST OF TABLES viii CHAPTER I. INTRODUCTION 1 1.1 Overview of Design Problem 1 1.1.1 Background 1 1.1.2 Current Design Model 1 1.1.3 Objective of Study 4 1.2 AISC Column Side Limit State Design Strength 4 1.3 Force Distribution Prediction 10 1.4 Scope of Research 11 CHAPTER II. EXPERIMENTAL INVESTIGATION 12 2.1 Scope of Test 12 2.2 Test Details 12 2.2.1 Test 1 Geometry and Design 12 2.2.2 Test 2 Geometry and Design 14 2.3 Instrumentation 14 2.4 Test Procedure 17 2.5 Test Results 17 2.5.1 General 17 2.5.2 Test 1 17 2.5.3 Test 2 21 2.6 Summary of Experimental Results 26 CHAPTER III. DEVELOPMENT OF FINITE ELEMENT MODEL AND COMPARISON WITH TEST RESULTS 28 3.1 Development of Finite Element Model 28 Page iv
3.1.1 Description of Finite Element Analysis 28 3.1.2 Shell Elements 28 3.2 Finite Element Results 29 3.2.1 Test 1 29 3.2.2 Test 2 29 3.2.3 Additional Finite Element Models 32 3.2.4 Parametric Study of Stiffener Sizes 34 3.3 Comparison of Experimental and Analytical Data 36 CHAPTER IV. DEVELOPMENT OF A DESIGN MODEL 38 4.1 Development of Effective Length 38 4.2 Load Distribution Between Column and Stiffener 42 CHAPTER V. SUMMARY AND RECOMMENDATIONS 45 5.1 Summary 45 5.2 Area Method Design Recommendations 46 5.3 Example Calculations 47 5.4 Recommendations for Further Research 49 REFERENCES 50 APPENDIX A. NOMENCLATURE 51 APPENDIX B. TEST 1 Results 54 B.1 Experimental Data 55 B.2 ABAQUS Input Data File 61 APPENDIX C. TEST 2 Results 66 C.1 Experimental Data 67 C.2 ABAQUS Input Data File 71 VITA 76 v
Figure LIST OF FIGURES Page 1.1 Moment Transfer Couple 2 1.2 Stiffener Force Based on AISC Manual Procedure 3 1.3 Local Flange Bending Stiffener Requirements 6 1.4 Local Web Yielding Stiffener Requirements 7 1.5 Effective Column Length and Load Distribution 11 2.1 Test 1 Specimen Geometry 13 2.2 Test 2 Specimen Geometry 15 2.3 Strain Gage Locations, Tests 1 and 2 16 2.4 Test 1 (W16x45) - Load vs. Micro-strain Results for Stiffeners R and L 18 2.5 Test 1 (W16x45) - Strain vs. Distance Results for Stiffener R 20 2.6 Test 1 (W16x45) - Strain vs. Distance Results for Stiffener L 20 2.7 Test 2 (W8x48) - Load vs. Micro-strain Results for Stiffeners R and L 22 2.8 Test 2 (W8x48) - Load vs. Micro-strain Results for Web R and L 23 2.9 Test 2 (W8x48) - Strain vs. Distance Results for Stiffener R 24 2.10 Test 2 (W8x48) - Strain vs. Distance Results for Stiffener L 24 2.11 Test 2 (W8x48) - Strain vs. Distance Results for Web R and L 25 2.12 Comparison of Stiffener Force Ratios 27 3.1 FE Model for Test Specimens 30 3.2 Finite Element Results for Stiffeners Stress vs. Distance - Test 1 and 2 31 3.3 Finite Element Results for Web - Test 2 32 3.4 W14x311 Finite Element Results 33 vi
3.5 W12x120 and W14x500 Finite Element Results 35 3.6 Comparison of Stiffener Force 37 4.1 Equivalent Load Distribution 39 4.2 Plot of Element Stresses W14x311 Specimen 40 4.3 Equivalent Column Web Load Distribution 41 vii
Table LIST OF TABLES Page 2.1 Force Distribution - Test 1 (W16x45) 19 2.2 Force Distribution - Test 2 (W8x48) 26 3.1 Stiffener Force from FE Models 32 3.2 FEA Results for Additional Column Sections 34 3.3 FEA Results for W14x90 Stiffeners 36 3.4 Predicted versus Test Results 37 4.1 Effective Lengths 42 4.2 Effective Area Values 43 4.3 Comparison of Results 43 viii