Highw ay parapets for bridges and other structures

BS 6779 4:1999 pdf free.Highw ay parapets for bridges and other structures一 Part 4: Specification for parapets of reinforced and unreinforced masonry construction.
To minimize the risk of hook-up of a vehicle, the front face of the pilaster shall be flush with the front face of the parapet. However, where a projection of the pilaster to the front face of the parapet is essential, the projection shall be limited to a depth of 75 mm and be splayed at an angle of 45° or flatter relative to the front face.
Where a recessed panel is required to the front face of a pilaster it shall be limited to 75 mm and the edges be splayed as required for projections.
Where a pilaster is located at a curved end on a parapet (see Figure 7) it shall not project or be recessed.
For unreinforced parapets if the interlocking bond pattern in the masonry units of the parapet is discontinued at the junction with the pilaster then shear connections shall be provided in accordance with 6.7.4.
6.6 Reinforced masonry parapets
6.6.1 General
Reinforced masonry parapets shall be designed generally in accordance with BS 5628-2, to resist loading appropriate to the designated level of containment using the equivalent static nominal loading from Table 2 for panel lengths up to and including 3.5 m. For parapets of greater panel length than 3.5 m, the forces and moments given in 6.6.3 shall apply. In all cases the design shall be checked against punching shear in accordance with 6.6.4.
NOTE 1 The difference between height for structural design considerations and parapet height is illustrated in Figure la) together with potential difference between top of parapet for height considerations and top of front face of parapet for impact considerations.
The parapet shall be attached to the supporting structure by appropriate attachments/anchorage such that all of the sustained loading is resisted by cantilever action. The attachment/anchorage system shall satisfy the design requirements of 6.6.9 with the partial safety factors of Table 3 and Table 4.
NOTE 2 Partial safety factors for attachment.slanchorages are enhanced with respect to those for parapet design to prevent failure occurring within the attachmentianchorage system with consequential damage to the supporting structure.
NOTE 3 The equivalent static nominal loads for the design of reinforced masonry parapets to high containment level are derived from strain measurements on the vertical reinforcement. From the strain values and observations of damage caused under test, a reinforced masonry parapet designed to the specific requirements of this part of BS 6779 should not require emergency replacement. Different levels of damage may be sustained by parapet systems designed to the specified requirements of other parts of this standard.
NOTE 4 Details of a reinforced masonry parapet design developed from a test carried out to a high level containment for British Rail by MIRA (Motor Industry Research Association) are given in Annex C. This design performed very satisfactorily under test and the values from the instrumentation attached to the wall have been incorporated in this standard.
NOTE 5 A typical strain graph of a high level containment test showing the recorded values in the vertical reinforcement is shown in Annex D. This serves well to illustrate the time scale of peak strains and the way the impact force is impacted in particular stages.
For parapet or panel lengths of 2.0 m to 3.5 m, the bending moments and shear forces to be resisted per unit length of parapet shall be in accordance with Table 2.
6.6.3 Parapet lengths greater than 3.5 m
For parapet lengths greater than 3.5 m the bending moments and shear forces to be resisted per unit length of parapet shall be derived from Table 2 assuming a panel length of 3.5 m.
NOTE The requirement to resist a minimum force of 110 kN/m for shear considerations for normal as well as high containment is to ensure that wall elements, such as coping units, are not detached under a severe impact at top of parapet level.
6.6.4 Punching shear
In order to prevent masonry becoming displaced from the outer face under punching shear, the shear on a defined perimeter throughout the wall thickness shall not exceed the allowable characteristic shear strength of masonry in accordance with BS 5628-2:1978, providing that f,, is not taken to be greater than 0.7 N/mm2.
For high containment the nominal punching shear force shall be a patch load of 255 kN applied over a circular area of 0.6 rn diameter at any position on the front face of the wall.
For normal containment the nominal punching shear force shall be a patch load of 150 kN applied over a circular area of 0.6 rn diameter at any position on the front face of the wall.
NOTE It may he assumed that the plane in which punching shear acts will be the circumfrrence of the patch load spreading at 45 to the wall face for the thickness of the wall.
6.6.5 Design method
The parapet and attachments/anchorages shall be designed by the application of limit state principles, as specified in 6.6.6. 6.6.7, 6.6.8 and 6.6.9, using appropriate partial safety factors, y, in accordance with Table 3.
NOTE The partial safety factors specified are intended to control damage at the designated level of containment such that displacement of material from the parapet is not a hazard to highway users or to the space usage beyond the outer face of the parapet.
Characteristic (or nominal) material strengths, f, and partial factors on material strength, Ym, shall be used in accordance with Table 4.
Attachment systems and anchorages shall be designed to resist the loadings given in 6.6.2 and 6.6.3 as appropriate.
In addition, attachment systems and anchorages for high containment parapets shall be designed to withstand the following coexistent nominal loads, Qk:
a) a nominal horizontal longitudinal load of 72 kN applied at the top of the front face of the parapet uniformly distributed over a length of 3.0 m, or for panel lengths less than 3.0 m, distributed over the length of the panel;
b) a nominal downwards vertical load of 175 kN uniformly distributed over a horizontal length of 3.0 m at the top of front face of the parapet or, for panel lengths less than 3.0 m, distributed over the length of the panel.
NOTE 1 Where attachment is achieved by vertical reinforcement bars within the wall core bonded into the supporting structure, couplers may be used to facilitate construction or any subsequent repair work.
Couplers shall be designed to transfer the full design loads, Q*, with the stipulated limit state factors, y, into the attachment bars in the supporting structure and shall be of a type which permits the replacement of the vertical reinforcement within the wall core.
Reinforcement shall be of Type 11 high bond type in accordance with BS 4449.
NOTE 2 For durability requirements see 7.2.7.
All vertical reinforcement bars shall continue for the full height of the parapet up to coping level. Horizontal distribution reinforcement bars shall be provided, at not less than 25 % of the area of vertical reinforcement, positioned on the outer face side of the vertical reinforcement.
Stainless steel bed joint reinforcement shall be provided in alternate courses of the masonry face work where this is brickwork and shall continue across the full thickness of the parapet to 20 mm from the external faces of the wall.
Where the masonry face is in stonework of a vertical depth of stone greater than 150 mm, bed joint reinforcement shall be provided at each course level.
The bed joint reinforcement shall provide an area of transverse reinforcement in each layer across the wall core of not less than 88 mm2 per metre length of wall. Across core reinforcement shall be structurally attached to longitudinal reinforcement secured within the bed joints of the masonry. The longitudinal reinforcement shall be so positioned that at least one bar is located in the outer third area of the bed joint, and shall have a minimum cross-sectional area of 19 mm2 per bar.
Bed joint reinforcement, where required to be accommodated within a 10 mm bed joint thickness, shall have an overall thickness of not more than 6 mm.
NOTE 3 As well as bonding the composite construction of the wall together, bed joint reinforcement is required to provide link reinforcement resisting horizontal shear. The specified minimum area is for a cross wire or bar at right angles to the wall face. Where the reinforcement is of the inclined lattice type an appropriate adjustment in sectional area is required.BS 6779 4 pdf free download.Highw ay parapets for bridges and other structures