The new SM1600 design loading of the draft Australian Bridge Design Code AS 5100 is complex. Modifications are suggested to the AS 5100 loading provisions for the design of box culverts, particularly in regard to live load surcharge and compaction pressure. The use of the accompanying lane factors, together with the different uniform lane loads associated with the M1600 and S1600 design vehicles, appears to add complexity to the design of large precast box culverts and other short span or buried structures that is not required for these structures. Accordingly, it is suggested that the SM1600 loading be modified with a view to simplifying it for the purpose of designing culverts and other short span buried structures, to a tandem or a triaxle loading applied without uniform lane load or accompanying lane factors. The adequacy of the current M1600 triaxle load is reviewed using available data from Culway sites, and the use of this data for verification and adjustments of design vehicle loads is briefly discussed. (a) For the covering entry of this conference, please see ITRD abstract no. E211602.

Design loads for box culverts for the SM1600 design loading of the Australian Bridge Design Code AS 5100

THE OBJECT OF THE LABORATORY EXPERIMENTS DESCRIBED HEREIN IS TO PROVIDE BASIC KNOWLEDGE CONCERNING THE MAGNITUDE AND DISTRIBUTION OF THE VERTICAL PRESSURES ON A SUBGRADE BENEATH A FLEXIBLE OR NON-RIGID TYPE OF PAVEMENT WHEN CONCENTRATED LOADS, SUCH AS TRUCK WHEELS, ARE APPLIED TO THE PAVEMENT SURFACE. A SYNTHETIC SUBGRADE OF DRY CLAY LOAM SOIL WAS CONSTRUCTED WITHIN A CONCRETE BIN 8 FT. SQ. IN. PLAN AND ABOUT 2.5 FEET DEEP. FLEXIBLE-TYPE PAVEMENTS WERE CONSTRUCTED ON THIS SUBGRADE OF TWO KINDS OF MATERIALS; ONE A STABILIZED GRAVEL MIXTURE AND THE OTHER A SAND-CLAY MIXTURE. THE THICKNESS OF THESE PAVEMENTS RANGED FROM 3 IN. TO 10 IN. LOADS WERE APPLIED TO THE SURFACE OF THE PAVEMENT AT THE CENTER OF THE 8 FT SQ AREA THROUGH A 7 BY 21, 6-PLY TIRE IN AMOUNTS RANGING FROM 1000 LB. TO 5000 LB. BY 1000 LB. INCREMENTS AND WITH THE TIRE INFLATED TO VARIOUS INTERNAL PRESSURES FROM 30 P.S.I. TO 70 P.S.I. BY 10 LB. OR 20 LB. INCREMENTS. THE VERTICAL PRESSURES ON THE SUBGRADE WERE MEASURED BY MEANS OF SMALL CARBON DISK PILES ARRANGED AT FREQUENT INTERVALS ALONG ELEMENTS PARALLEL TO THE MAJOR AND MINOR AXES OF THE TIRE CONTACT AREA. IN ADDITION TO THE SUBGRADE PRESSURE MEASUREMENTS, AN EXTENSIVE STUDY WAS MADE OF THE RELATION BETWEEN THE CONTACT AREA BETWEEN THE TIRE AND THE PAVEMENT SURFACE AND THE LOAD ON THE TIRE AND THE TIRE INFLATION PRESSURE. THE DATA TAKEN INDICATE THAT, IN THESE EXPERIMENTS, THE SUBGRADE PRESSURE IS DISTRIBUTED IN ACCORDANCE WITH THE TYPICAL HELMET-SHAPED SURFACE OF THE CLASSICAL BOUSSINESQ SOLUTION; THAT THE MAXIMUM PRESSURE OCCURS ON A SMALL AREA OF THE SUBGRADE DIRECTLY BENEATH THE LOAD; THAT THE MAGNITUDE OF THIS PRESSURE MAXIMUM IS INDEPENDENT OF THE TIRE INFLATION PRESSURE, NEARLY DIRECTLY DEPENDENT UPON THE APPLIED LOAD, AND INVERSELY PROPORTIONAL TO THE THICKNESS OF THE PAVEMENT; AND THAT THE LOAD- INFLATION PRESSURE QUOTIENT IS NOT A VALID CRITERION FOR DETERMINING THE AREA OF CONTACT BETWEEN A TRUCK TIRE AND A FLEXIBLE PAVEMENT. /AUTHOR/

Wheel load stress distribution through flexible type pavements

This paper presents a more fundamental understanding of the nature of live load induced horizontal earth pressure and its interaction with earth pressures caused by fill and compaction. 'Live load surcharge' horizontal earth pressure is shown to be the cumulative and residual resultant of priors loading history, including loading during construction. Consequently, live load induced horizontal earth pressure can exist without concurrent loading by traffic wheel loads. This is in marked contrast to the traditional treatment of live loads in structural design codes. This new concept has considerable implications for the design and construction of box culverts, abutments, and retaining walls. Design expressions are given for the horizontal pressure due to the AUSTROADS T44 Truck Loading and the Heavy Load Platforms.

V Nechvoglod

Papers

Horizontal earth pressures on box culverts, abutments and walls due to wheel loads