RATIONAL DESIGN OF BEAM AND SLAB HIGHWAY BRIDGES

DESIGN SPECIFICATIONS FOR HIGHWAY BRIDGES ARE REVIEWED. IF THE TYPE OF STRUCTURE TO BE USED IS KNOWN, THE DESIGN PROCESS INVOLVED THE FOLLOWING DECISIONS AND PROCEDURES: (1) DETERMINATION OF LIVE LOADS, (2) DETERMINATION OF MARGIN OF SAFETY TO BE PROVIDED, (3) PROPORTIONING OF THE STRUCTURE IN LIGHT OF THE PREVIOUS DETERMINATIONS, (4) VERIFICATION OF SERVICEABILITY OF STRUCTURE, AND (5) MODIFICATION OF DESIGN IF NECESSARY TO ENSURE BOTH SERVICEABILITY AND THE REQUIRED MARGIN OF SAFETY. THE RELEVANCE OF LIMIT DESIGN NEEDS ARE REVIEWED IN PROBLEMS RELATED TO SIMPLE BEAM AND SLAB BRIDGES. IN LIMIT DESIGN, IT IS POINTED OUT THAT THE SAFETY FACTOR REPRESENTS THE TOTAL ALLOWANCE BEING MADE FOR VARIOUS CIRCUMSTANCES WHICH MAY AFFECT THE SAFETY OF THE STRUCTURE. THE PRINCIPAL FACTORS INVOLVED ARE: (1) THE POSSIBILITY OF OVERLOAD, (2) LACK OF PRECISION IN DESIGN CALCULATIONS OR LACK OF CONFIDENCE IN BASIC ASSUMPTIONS, (3) THE POSSIBILITY OF DEFICIENCIES IN MATERIALS, (4) THE POSSIBILITY OF MINOR ERRORS IN CONSTRUCTION WHICH MAY REDUCE THE STRENGTH, AND (5) THE POSSIBILITY OF FAILURE OF THE WHOLE STRUCTURE RESULTING FROM FAILURE OF ONE PART. SAFETY FACTORS ARE SUGGESTED FOR THE DESIGN OF HIGHWAY BRIDGES. THE FOLLOWING MATTERS ARE DISCUSSED WHICH MUST BE CONSIDERED IN ASSESSING THE BEHAVIOR OF A BRIDGE UNDER NORMAL WORKING LOAD CONDITIONS: (1) THE STRESS RANGE IN CONCRETE AND REINFORCEMENT MUST BE SUCH THAT FATIGUE FAILURES WILL NOT OCCUR, (2) THE WIDTH OF CRACKS SHOULD BE SUFFICIENTLY SMALL SO THAT DETERIORATION OF CONCRETE AND OF REINFORCEMENT WILL NOT OCCUR, (3) THE BRIDGE MUST NOT VIBRATE IN SUCH A WAY AS TO CAUSE DISQUIET, AND (4) DEFLECTIONS FROM BOTH LIVE AND DEAD LOAD SHOULD NOT BE NOTICEABLE. NO DEFLECTION LIMITS ARE REQUIRED IN MODERN CONCRETE BRIDGE SPECIFICATIONS. IT IS NOTED THAT LIMIT DESIGN CRITERIA APPLIES ONLY WHEN SUFFICIENT ROTATION AT HINGES AND YIELD LINES CAN TAKE PLACE.

• Supplemental Notes:
  • Vol 51, No 9, PP I-XII, 5 FIG, 1 TAB, 21 REF
• Authors:
  • Lash, S D
• Publication Date: 1968-9

Media Info

• Serial:
  • Engineering Journal /Canada/

Subject/Index Terms

• TRT Terms: Bridge construction; Bridge design; Bridge foundations; Bridges; Concrete; Construction; Deflection; Design standards; Durability; Highway bridges; Live loads; Material reinforcement; Oversize loads; Proportioning; Reviews; Safety factors; Serviceability; Slabs; Specifications; Stresses; Structural design; Ultimate load design
• Uncontrolled Terms: Overloads
• Old TRIS Terms: Stress conditions
• Subject Areas: Bridges and other structures; Construction; Design; Highways; Safety and Human Factors;

Filing Info

• Accession Number: 00208871
• Record Type: Publication
• Files: TRIS
• Created Date: Mar 18 1994 12:00AM