Author: Mezie Ethelbert

Reading Time: 4 minutes Prior to the construction of overlying layers of pavement, it is necessary to determine the subgrade surface modulus of the foundation. Different moduli are encountered in foundation design for pavement but each is drawn from the stiffness modulus which is the ratio of applied stress to induced strain. Our focus would be on the subgrade surface modulus which is an estimated value of ‘Stiffness Modulus’ based on subgrade CBR and used for foundation design. The Subgrade Surface Modulus used for design must be determined using the lowest value of the long term and short term CBR. See Figure 1 for…

Reading Time: < 1 minute This procedure shall be used at the top of a pavement foundation to measure and provide limitations to deformation in the foundation under construction trafficking. Apparatus Required (i) Straight edge with a minimum length of 2 m; (ii) Two identical blocks; and (iii) Ruler. Procedure 1. Place a straight edge transverse to the rut and raise it clear from the rut by two identical blocks. The blocks shall be placed on undisturbed material outside the wheel path. 2. Measure the amount of deformation as the difference between the foundation at (A) and the height of the blocks at (B). Note…

Reading Time: 5 minutes Hydraulic structures are very important in pavement construction in order to prevent the sub-base or subgrade of the pavement from getting saturated. This is more onerous as the axle loads of the pavement due to modern traffic increases. If there is not adequate drainage for the pavement, surface water can enter the pavement construction though: i. The porous surface ii. Cracking as the pavement ages and iii. At the edge of the carriageway if it cannot enter gullies grips or edge drainage easily. Wherever possible, drainage through grips to ditches, kerbs and channels or continuous channel drainage should be provided.…

Reading Time: 3 minutes Prior to the design of piles and pile caps, the working load of the pile is estimated. A pile is known to bear load by either skin friction or end bearing or both. These mechanisms of load bearing for the pile are considered when determining the pile working load. Other parameters required for this design such as the soil unit weight, the underlying soil across the stratum of installation and their depth, the depth to the water table, etc are all determined from soil tests carried out for the location. Example The figure below is the column application plan of…

Reading Time: 7 minutes Trusses resist axial forces (member forces) only. These forces are usually tension and compression forces. A typical example of a truss member is the roof truss with members such as kingpost, rafters (in roof truss) or boom in other usage, tie members (and not tie beams), etc. The first step in the analysis of a statically determinate structure is to determine the support reactions. This can be done either by using the equations of static equilibrium or by the funicular polygon. Afterward, the determination of the member forces can be accomplished by either of the following methods: Method of Joints…

Reading Time: 2 minutes The following table provides a guide on the values of minimum superimposed floor loads to be used for the structural design of buildings and other simple structures according to the Nigerian Code of Practice (NCP 1: 1973). Class Type of Floor/Building Load (kN/m2) 1 Private dwelling not exceeding two (2)storeys in height 1.43 2 Private dwelling exceeding two (2) storeys in height; floors other than those in private dwellings, used for residential purposes; hospital wards and rooms. 1.96 3 Rooms used as offices – floors above entrance floor only. 2.46 4 Classrooms in schools and colleges. 2.94 5 Rooms used…

Reading Time: 6 minutes Accurate loading of buildings is necessary if accurate analysis and design would be carried out for the building. In the loading of structures, two types of load are encountered, dead load (BS 8110) or permanent action (EC 2) and live load (BS 8110) or temporary action/imposed loads (EC 2). For all types of structures, these two loads are encountered. Permanent actions chiefly consist of the self-weight of the structures or construction works. Self-weight is usually represented as single characteristic value or estimated as the product of the nominal dimensions as shown on the drawings of the structural elements, non-structural elements,…

Reading Time: 4 minutes California Bearing Ratio (CBR) is a very important test used to access the strength of soil prior to construction. Though many new pavement structural design methods such as: empirical-mechanistic and mechanistic methods that are based on stresses are being developed, CBR is still being identified as the best indicator of soil strength despite some challenges in its measurement especially with mixed fine and coarse graded materials. Factors that Contribute to Failure of Subgrades Although subgrade CBR value and design traffic are solely employed in most empirical design formulas to determine the thickness of the pavement layers, it is also necessary…