Code of practice or standards can be defined as a set of written regulations issued by a professional association or an official body that explains how people working in a particular profession should be guided. A code of practice helps workers in a particular profession to comply with ethical, safe and healthy standards. The Design and Construction Standards, comprised of the Design Criteria, Technical Specifications and Supplemental Standards (Project Specifics).
Civil Engineering is a diverse profession whose branches are many. To see the different branches of civil engineering and their specialization, click HERE. Civil engineering is not fully defined without mentioning design. From design to consultancy to maintenance, a civil engineer is important for an infrastructure. Design codes and standards guides highway design, design of reinforced concrete elements, design of steel structures, masonry structures, timber design etc. Two aspects of design that is very common in Nigeria which are reinforced concrete design and highway design would be treated.
Reinforced Concrete Design
In Nigerian tertiary institutions, design of various structural elements are usually taught using inherited international codes of practice common in the Britain previously and most recently the British annex of relevant European codes. For instance, design of reinforced concrete elements in Nigeria was previously based on BS 8110 and most recently on the UK annex of Eurocode 2 (BS EN 1992 1-1 $ 1-2). In a previous post titled Design standards and codes, I showed different design codes and their equivalent in other international standards. Civil engineering students and practitioners often come to believe that there is no indigenous standards for design of structural elements in Nigeria. Their conviction could be buttressed by the fact that no Nigerian design code is taught in the undergraduate design courses and none is available in the popular design softwares used in Nigeria for structural design of reinforced concrete elements. CSC Orion 18 design suite have design codes from Hongkong, Ireland, United Kingdom, Singapore and Malaysia etc. This software is among the most popular for structural design in Nigeria but no Nigerian code is available in it. Other design softwares like Staad Pro V8i and Staad Connect edition, SAP 2000, Etabs etc that have even more variety of codes does not contain any Nigerian code. Another popular software Civil Soft design suite which was produced by a Nigerian was not based on any Nigerian code. Therefore, the disbelief of young Nigerian students cannot be faulted.
Contrary to this popular belief, Nigeria have standards for design of structural elements. Standards Organization of Nigeria (SON) have the following Nigerian Industrial Standards (NIS) for design of structural elements in Nigeria:
- NIS 197: Specification for structural steel.
- NCP 01:1973 Structural use of concrete in building Pt-l and NCP 01:1973 Loading. Pt-3.
- NIS 156: Standard method of testing fresh concrete.
- NIS 12:1974: Methods of testing concrete.
- NIS 13:1974: Specification for aggregates from natural source for concrete.
- NIS 117:1992: Steel bars for the reinforcement of concrete.
- NIS 87:2000: Specification for sandcrete blocks
These standards which may have undergone review, list out the comprehensive requirements, testing procedure and acceptance criteria for each kind of project work. The young engineers and site supervisors should be well aware of these standards in relation to their trade of work by studying the requirements from time to time when they meet the terms in the drawings and specifications. The standards can be downloaded from Standards Organization of Nigeria (SON) website.
The application of these codes just like other international codes can be found in
Loading and Load Combinations
Allowable Material Stresses and Capacities.
Choice of Foundation
Allowable serviceability Limits
Building Structural Element Design.
Floors, Beams, Columns & Foundations.
Reinforcement Detailing –Fitting Together the Structure.
Falsework & Other Construction Consideration
It is important that these codes and standards are also used to teach students in undergraduate studies in Nigeria and to make comparison of such codes with international codes. Since softwares are highly acceptable in design of structural elements in the world presently, it is important that the Nigeria Society of Engineers (NSE), make effort to ensure that these codes are integrated into design softwares used for design of structural elements in Nigeria.
There are a lot of manuals that guide highway designs in Nigeria. In a post titled: Different aspects of highway design, I showed the different kinds of designs common in highway works. These include: structural (thickness) design, geometric design, materials design, hydraulic design etc. The Nigerian Highway Manual contains guides for highway design and maintenance in Nigeria and all the aspects of design are covered. In my undergraduate, I was taught estimation of design traffic based on Design Manual for Roads and Bridges (DMRB) of UK even when there is Nigerian Highway Manual that shows how this can be done. It is important that these manuals are made available to Nigeria student civil engineers so that they would be enlightened about design standards and codes in Nigeria. The chart below shows layout of contents of Nigeria’s Highway Manual while figure 1 shows typical layout of pavement.
“…the Manual aims to guide members of staff of the Ministry and engineering practitioners, with regard to standards and procedures that the Government deem acceptable; to direct practitioners to other reference documents of established practice where the scope of the Manual is exceeded; to provide a nationally recognized standard reference document; and to provide a ready source of good practice for the development and operation of roads in a cost effective and environmentally sustainable manner.”
NB: The Manual is in two parts-Design (Part 1) and Maintenance (Part 2)
Geometric design also called route design is about the location of the road with respect to other adjoining features. The setting-out of curves (horizontal, vertical and transition curves) are all carried out under geometric design. In the geometric design manual, the width of roads, width of shoulder elements and other geometric profile elements such as minimum grades and cross slopes (respectively) required for good drainage are provided. You can visit Road classification systems in Nigeria for more. You can download the manuals online or text the author for some of the manuals.
The pavement and materials design is concerned about using the suitable materials in the pavement construction. A lot of tests are conducted here to ensure that suitable soils are used. When bad soils are encountered such as collapsible soils or expansive soils (e.g. black cotton soils), they should be stabilised if possible or removed entirely and replaced with better soils. For instance,
A soil is considered to be potentially expansive and requires extended investigation if:
- Field visits confirm expansiveness
- PIw is greater than 20%
Where, PIw= PI (% Passing the 425mm)/ 100
Classification tests and strength tests are very useful here.
Structural designs are usually about thickness of various layers of the pavement. In Nigeria, CBR design method is still common where the subgrade CBR and traffic survey data are the input parameters.
The hydraulic design is of critical importance in the design of highway because water egress to subgrade of pavement or other layers leads to early failure of such pavement. Good hydraulic design involves consideration of roadway gutter, median and inlet capacities. Inlet and outlet control nomographs are used for hydraulic design depending on the parameters given. Headwater (HW) can be determined when the culvert size (D) and discharge (Q) for pipe culvert or Q/B for box culvert are known. The culvert size can be determined when HW/D value are known. The discharge (Q) can be determined when HW and D values are known. In most cases, the hydraulic design of pavement begins with hydrological analysis through which the design discharge (Q) are determined. I would not go deep into explaining this as it does not form the scope of the post. Following the hydrological analysis is the determination of the culvert size (D). The nomographs are available for both box and pipe culverts. In a subsequent post I would show how to use nomograph to size pipe culvert. Figure 2 shows typical inlet and outlet nomograph for pipe culvert.
Softwares for hydraulic design
There are several public domain hydraulic design software programs that are available for free download from the internet and can be used to simplify and streamline the hydraulic design process for pavement. Example of such are:
1. HY-8: This wasdeveloped by the US Federal Highway Administration (FHWA). It is a culvert design software program that can be freely downloaded from the FHWA website (www.fhwa.org) and is classified as public domain software.
2. HEC-RAS: HEC-RAS is a public domain software program developed by the US ArmyCorps of Engineers for the calculation of water surface profiles in openChannels, etc.
At present, I don’t know whether there is any specific code for geotechnical design, timber design, aluminum design and other specialized designs in Nigeria. Such designs at present are based on inherited international standards.
Engr Alieme Unuigbe of Nigerian Institution of Structural Engineers (NIStructE). Paper presented at the NSE codes and standards committee virtual workshop.
Engr. Fadeyi L. Olaniyi of Nigerian Institution of Civil Engineers (NICE). Paper presented at the NSE codes and standards committee virtual workshop.