measurement and cost management of concrete...
TRANSCRIPT
MEASUREMENT AND COST MANAGEMENT OF CONCRETE BRIDGES
Presented by:
Parkinson Enina Erhunse MNIQS, RQSProcost Consult, Box 1228, Gombe, Gombe State.
( GSM No: 08032866662 )
In Nigerian Institute of Quantity Surveyors (NIQS) 2-Day National Training Workshop with the Theme: “Measurement and Cost Management of Engineering Infrastructure
Projects” held at Universal Hotel, Plot 3, Aguleri Street, Independence Layout by WAEC Junction, Enugu on 30-31st July, 2015.
Abstract• The paper examined the inadequacies of measurements and cost
management of concrete bridges and by extension civil and heavy engineering projects using a concrete bridge project in the North East Geo-Political Zone in Nigeria. The paper did an exposition on classifications of bridges, component parts of concrete bridges and construction works; it included tables, plates and figures. The paper also highlighted standard methods of measurements, over-view on cost management and in addition show-cased an example of a typical BEME format. The paper emphasized the need to fill inadequacies in measurements and cost management of concrete bridge, by engaging quantity surveyors to complement the roles of engineers on engineering projects generally; this will further enhance Value-for Money for the client.
Introduction
A bridge is a structure that provides passage facilities over an obstacle without closing the way underneath. The required passage may be for a railway, road or pedestrian walkway and so forth. The obstacle to be crossed may be deep valley full of water, river and so forth (Gupta and Gupta, 2008).
Simply put, a bridge is a structure that is built over a gap in order to provide a hindrance free beneath. Bridges could be built over a river crossing a proposed road, gorge, and railway/railroad as well as over an existing road and footpaths. The origin of a bridge could be traced to felling of tree trunks over a stream.
According to Brierley and Fryirs (2008), ‘Rivers are part of society’s lifeblood. We live along these natural arteries of the landscape, and they provide fundamentally important services: ready access to potable water, an easy means of transportation, fertile and replenished lands readily irrigated for agricultural use and a reliable source of renewable energy. The earliest form of permanent bridges was built over the Nile River by Menes, the first king of the Egyptians, about 2650 BC. About 4000 years ago, a remarkable bridge with a timber deck on stone piers was built over the River Euphrates in Babylon.Ponnuswamy (2013) reported that the oldest bridge, according to Swedish Institute of Construction, was a wooden bridge built in England in 3306 BC. Continuing, he reported ‘The Chaldeans and Assyrians developed the brick or masonry arch; this was further developed in the western world and later distributed to places like China, Middle East and Mexico’.
Liebenberg (1992) reported ‘The Greeks and the Romans used timber for less permanent structures, timber trestle bridges were developed for military purposes. The Renaissance period witnessed the development of truss system based on the principle of triangles, which cannot be deformed’.It worthy to note that Russians used timber as main bridge building material up to the end of the 15th century; while some other parts of former Union of Soviet Socialist Republic (USSR) built masonry bridges. The 18th and 19th centuries witnessed the trend for longer span bridges, especially in the United States of America (USA), this led to building of cable suspension bridges, the Golden Gate Bridge in San Francisco bay in USA built in 1937, is an elegant example of such structures. Japan built the longest cable suspension bridge, Akashi Kaikyo Bridge, with a record span of 1991m as on date. Germany was the first to introduce the concept of cantilever construction and incremental launching of concrete decks, as well as modern form of cable strayed bridges. China was equally noted to have built bridges using tied arch form and stayed cables’.There are numerous reinforced concrete bridges that dot several parts of Nigeria, for example: The Third Main-Land Bridge, River Gongola Bridge at Numan and of course Lagos Street Bridge in Maiduguri, Borno State.
The provision of a bridge involves consideration for the following: Investigation Conceptualization Planning Execution MaintenanceFor the purpose of this paper, it is assumed that full investigation, conceptualization and planning required for a concrete bridge have been concluded and that the provision of the concrete bridge is at the execution stage.
Each project is an entity in itself; it is organized to achieve its mission, within pre-determined objectives; project mission is expected to be achieved within the project time, cost and quality (Chitkara, 2011).
Classification of BridgesThere are various classifications of bridges, Ponnuswamy (2013) postulated the broad classifications and sub groupings are as indicated in Table 1.
S/No Main Classification Sub Classification
1 Function Foot; Road; Railway; Road-cum-rail; pipe line; water conveying (aqueduct); jetty (port).
2 Material Stone; Brick; Timber; Steel; Concrete; Aluminum; Fibre composite.
3 Form Slab; Beam; Arch; Truss; Suspended; Cable supported.
4 Type of support Simply supported; Continuous; Cantilever. 5 Position of floor/deck Deck; Through; Semi through.6 Usage Temporary; Permanent; Service (Army).7 With respect to water
levelCauseway; Submersible; High level (Normal case).
8 Grade separators Road over; Road under (Sub-way); Fly over (Road over road).
9 With respect to connections (Type of jointing)
Pin jointed; Riveted/Bolted; Welded.
10 Movable bridges (Over navigation channels)
Bascule; Lifting; Swing.
11 Temporary bridges. Pontoon; Bailey; Light alloy portable bridges developed by Army.
Table 1: Classification of Bridges.
Plate IV: Cable-supported Bridge (Ikoyi-Lekki Bridge, Lagos).
Plate V: 7-span concrete bridge located at Futuk, Gombe State
Plate VI: 7-span concrete bridge located at Futuk, Gombe State
Plate VII: 7-span concrete bridge located at Futuk, Gombe State
Plate VIII: Soffit of 7-span concrete bridge located at Futuk, Gombe State.
Plate IX: 6-span concrete bridge located at Tumu, Gombe State.
Plate X: 6-span concrete bridge located at Tumu, Gombe State.
An Outline of Lagos Street Bridge, located in Maiduguri
• The peculiarities of the bridge in this case study inspired the writing of this seminar paper. These include: Security threats common to the geo-political zone location of the bridge work at the time of construction; excessive haulage distances of construction materials; difficulties in sourcing willing labour-force, especially specialist for piling work; difficulties in sourcing some plant items, such as heavy duty cranes and so forth.
• The Lagos Street bridge work, an 8-span (120m long) bridge, was packaged with the road project contract, which was awarded in May 2012 with an initial contract period of two years. The value of the bridge was about 30 percent of the entire road contract sum. The main contractor mobilized to site as stipulated, however progress on the project has been disrupted intermittently. The bridge construction work was partly delayed due to re-alignment of the proposed road and force majeure. Presently the bridge has attained about seventy-five percent completion. It is important to mention here that this resource person has participated in the construction and successful completion of some concrete bridges (See Plates V – X). The followings are highlights of some progress made on Lagos Street Bridge, Maiduguri. Plates XI – XIII.
Plate XI: Partial view of piers and transverse beams.
Plate XII: Steel casings (Precast longitudinal beams in the background).
Plate XIII: Precast Longitudinal Beams.
Major parts of a Concrete Bridge
The two major parts of a concrete bridge are:1. Substructure.2. Superstructure.
The substructure of a concrete bridge consists of three elements, namely:a) Foundationb) Piers and Abutmentsc) Wing-walls.
The foundation is that part of the bridge that transmits the loads from the piers and abutments/wing-walls and evenly distributes to the underlying strata. The soil type determines the type of foundation for a bridge; while raft foundation could be used for a foot-bridge to be constructed on a firm ground, the same cannot be used for a bridge across a river. There are principally three types of soils, namely:
Cohesive soils: These include soft shale, hard or stiff clay and firm clay.
Non-cohesive soils: These include Gravel (coarse and fine), fine sand, medium gravel and coarse sand.
Rocks: These include hard rocks, sandstone hard shale and soft rock..
Piling is obviously the most suitable foundation for cohesive soils and beds subject to minimal scouring; where piling is done, the gang of piles in one location that are to transmit loads for a set of piers are linked with a reinforced concrete pile cap.
Piers and abutments simply put are vertical structures that are to transmit loads from the superstructure to the foundation and thereafter distribute the load evenly to the underlying strata. A single span bridge does not have piers; the essence of piers is to break the entire bridge span to an effective structural span, in the case of Lagos Street Bridge project is 15m. The major difference between piers and abutments is that abutments are at the ends of a bridge, whose function is to provide vertical structural support to the superstructure as well as retain the earth behind; while piers are located between the abutments of a bridge.Wing-walls and returns are extensions to the abutments and they equally retain the earth of the approach bank.
Plate XIV: Formation of steel reinforcement bars for pile cap.
Plate XV: Formation of steel reinforcement bars for pile cap.
Plate XVI: Formation of steel reinforcement bars for pile cap.
Plate XVII: Shuttering to sides of pile cap.
Plate XVIII: Shuttering to sides of pile cap.
Plate XIX: Completed reinforced concrete pile cap.
Plate XX: Pile steel casings.
Superstructure: This is the part of a bridge that is easily visible, especially bridges that have low head-rooms. The superstructure of a bridge bears the loads passing over it and transmits same to the substructure. Superstructure elements of a bridge comprise of the followings: slab, railings, transverse beams, longitudinal beams, plinths and bearings.
Slab: This is the most visible part of a concrete bridge. It bears the loads passing over it and transmits same to other superstructure members. Slabs could be solid or voided. Solid slab comprises of false shuttering slabs (slender reinforced concrete slabs placed between longitudinal beams). After placing the false shuttering and complimentary reinforcement bars, in-situ concrete is then poured to compliment the required thickness of the solid slab. Voided slabs are for longer span of about 30m.
Railings: These are crash barriers that protect both sides of the bridge. Railings could be of reinforced concrete up-stands, steel railings or a combination of both.Transverse beams: These are the structural members cast over piers in each location.Longitudinal beams: These are those structural members that span between transverse beams along the length of the bridge. They are precast elements that are launched in their permanent place after attaining the required strength and at the time of need. The upper part of a longitudinal beam is exposed, with the reinforcement protruding, in order to connect it to the slab.Plinths: These are the reinforced concrete members casted on transverse beams. The number of plinths on each transverse beam is determined by the number of the ends of longitudinal beams they are to receive. Plinths heights slide both ways, with the highest height at the centre of the slab and sliding downwards both ways.
Bearings: Raina (1993) postulated that ‘bearings’ means the objects provided under the simply supported suspended spans for transmitting the loads from them to the supporting structure. The two types of bearings are free bearings and fixed bearings. Free bearings are used particularly on steel plate girder (railways bridge), usually provided with end strips on both ends of the bridge including a stopper at one end. Fixed bearings are elastoplastic and accommodate temperature variation; fixed bearings are fixed on concrete plinths.
Pedestrians walkway: This is also referred to as sidewalk; it is a raised platform along both sides of a bridge for use by pedestrians. Kerbsline is used often to demarcate pedestrian walkway from the bridge main carriageway. Pedestrains walkway often have PVC (Polyvinyl Chloride) pipes underneath to accommodate existing and/or future services.
Plate XXI: PVC drain pipes in concrete bridge located at Futuk, Gombe State.
Figure 1: Some parts of bridge superstructure.
Piling
• There are three different types of piles, these are: Bearing piles, friction piles and combination of friction and bearing piles (Ponnuswamy, 2013).
• Bearing Piles: These are piles designed to transmit load to the foundation strata directly taking into account the frictional resistance offered by enclosing soil; such bearing piles are generally taken up to or into the hard strata, such as soft or hard rock, hard consolidated sandy soil or gravelly soil.
• Friction Piles: These are piles designed to transmit the load through friction offered by the surrounding soil. Such piles can be provided in cohesive soils not subject to heavy scouring.
• Combination of Friction and Bearing Piles: These are piles designed to transmit the load both by friction of the surrounding soil and the bearing resistance of the founding soil at the tip of the pile. This type of pile is used in mixed types of soils.
Bearing Piles
• Bearing piles can be classified into two categories, namely: Displacement piles and non-displacement piles. Non-displacement piles are further classified as: Grout intruded; percussion; rotary bored and continuous flight auger. Rotary bored piles are further classified as: Large diameter and small diameter. Large diameter bored piles are further classified as: Straight shafted and under-reamed (Thornton, 1992).We shall be concentrating on straight shafted large diameter rotary bored piling.
• Bored cast in-situ piles entail the formation and casting of large diameter bored piles. The boring is carried out using tracked crane supported with hydraulic ram which operates a Kelly bar and rotary bucket drill. In non-cohesive soils formation, a casing (steel lining tube) and driven into the borehole with the help of a bailer when the desired level is attained. Bentonite slurry is used during excavation in order to keep the soil walls stable. The borehole is flushed, reinforcement cage is then lowered into the hole and tack welded to support bars at the top of the casing. Immediately the reinforcement cage is lowered, a tremie pipe is lowered into the borehole and concrete is poured into the tremie until concrete reaches the top of the casing. The tremie pipe end should always be below the top level of rising concrete. When concreting is completed, the tremie pipe and the steel casing are removed. However, in cohesive soils formation, only 3-4m of casing is used.
• Plates XXII - XXVIII show some of piling operations carried out on Lagos Street Bridge.
Plate XXII: Boring of a pile borehole.
Plate XXIII: Pile steel casing.
Plate XXIV: Lowering a pile steel reinforcement cage.
Plate XXV: Lowering a pile steel reinforcement cage.
Plate XXVI: Flushing pile borehole.
Plate XXVII: Flushing pile borehole.
Plate XXVIII: Top of a pile reinforcement cage lowered into steel casing.
Measurement of Concrete Bridges
• Measurement of concrete bridges and by extension many civil and heavy engineering works, require the active participation of quantity surveyors, more than what is obtainable presently. One of the principal reasons is that quantity surveyors, with their knowledge base in measurement, would contribute tremendously in arriving at more realistic quantities as well as contribute in providing the client the desired value for money.
• Measurement of concrete bridges, among others, requires the one measuring to study drawings and specification as well as have understanding of same, before embarking on measurements.
Quite a number of quantity surveyors prefer measuring building works rather than civil and heavy engineering works; this vacuum needs to be filled. Quantity surveyors’ participation in civil and heavy engineering projects collaborate the roles of engineers; engineers are designers and supervisors of engineering projects. Therefore, there is the need for improved synergies of the regulatory bodies of quantity surveying and engineering professions regarding measurement and costing of civil and heavy engineering projects. Presently, a sizable number of quantity surveyors are engaged on civil and heavy engineering projects by contracting firms.Measurement of construction works generally should be carried out in accordance with the most suitable method of measurement. The Standard Method of Measurement (SMM) or its Nigerian version, the Building and Engineering Standard Method of Measurement (BESMM) is being used predominantly to measure building works as well as some engineering works ancillary to building projects; however, the Civil Engineering Standard Method of Measurement (CESMM) has an advantage over the SMM/BESMM in the measurements of most civil and heavy engineering works, such as bridge works. The quantity surveyor should therefore have working knowledge of CESMM.
• Measurement of a concrete bridge work includes the following:• General items: These include: Contractual requirements; specified
requirements; method-related charges; provisional sums and prime cost items.
• Site investigation: This include: Trial holes and shafts; boreholes; pumping test wells; samples; site tests; laboratory tests and site instrumental observations.
• Geotechnical and other specialist processes: These include: Drilling for grouting through material; grout materials and injection; diaphragm walls; temporary ground anchors; permanent ground anchors and sand drains.
• Demolition and site clearance.• Earthworks.• Piling. • In-situ concrete and ancillaries.• Precast concrete.• Miscellaneous metalwork.• Pavement.
The measurement of a concrete bridge is an easy task when the measurer adheres to measuring document rules as well as has understanding of the drawings, specification and the technology guiding the work. The current nomenclature for bill of quantities for civil engineering works is Bill of Engineering Measurement and Evaluation (BEME). The BEME currently used for public civil engineering works, including a concrete bridge, does not reflect adherence to CESMM. For example, the general items exclude provision for contractual requirements and adequate method-related charges (if any) for the contractor. A typical BEME for a concrete bridge is as included at the end of this paper; while some parts of the working drawings are as in Appendices I-XI.
Cost Management of Concrete BridgesCost management of a concrete bridge emanates from realistic estimate at the planning stage. Estimating of bridges are simpler than that of building, but the beginners find building easier because they are familiar with the parts of building than they are with those of bridge (Dutta, 2010); while Vazirani and Chandola (2013) remarked that an estimated cost is the cost of that work estimated on the basis of drawings and specifications. However, Seeley (2010) opined that cost management can be defined as synthesizing traditional quantity surveying skills with structured cost reduction or substitution procedures using a multi-disciplinary team.Bridge construction is generally a specialist work; although the main contractor may have a bridge(s) included in his contract award for a road project; the construction of a bridge is usually sub-contracted to specialist bridge construction firms.
Bridge construction is risky and a prudent main contractor would distribute this risk to a competent domestic sub-contractor when there is no nominated sub-contractor; especially the piling work. Effective costing of a concrete bridge is vital to guide the main contractor in engaging a sub-contractor for a bridge work, either in part, such as piling work or whole, in that the entire bridge. There are indicators that there is inadequate guide for effective cost management of a concrete bridge; for example: omnibus rate is inserted in the BEME for concrete and formwork, measured in a single unit in cubic metre. Concrete elements assume different shapes and cross-sections; concrete members could be expressed in volumes, but same cannot be said for related formworks for such differing concrete elements, in terms of their shapes and cross-sections. Formwork required in each concrete element ought to be treated separately in terms of their differing formwork contents.
Cost management of bridge work is a function of a realistic estimate. Smith and Bower (1995) postulated that the record of cost management in civil engineering construction industry is not good; many projects show massive cost and time over-runs; these are frequently caused by underestimates rather than failures of cost management or contract administration. Estimates are predictions, the best approximation attainable; it will be unrealistic to expect estimates to be accurate, especially at the pre-tender stage. The realism of estimates depends largely on the following: Nature of the work Location of the work Level of definition of the work Level of risk Uncertainty at the time of preparing the estimate.
Distinguishing Cost and PriceSmith (1995) postulated that cost is the cost directly attributable to an element of work, including direct overheads: for example, supervision; while price is the cost of an element of work, plus allowance for general overheads, such as: insurances, taxes, cost of finance and profit.The cost of an element comprises of direct costs of materials in the permanent work as well as time-related costs and fixed costs. The cost of hiring a plant item is a fixed cost; while the costs of operating a plant item and related labour are time-related. The above relationships can be represented as below:
Cost = Cost of materials + cost of labour/plant + direct overhead
Price = Cost + mark-up(Where mark-up includes: General overheads, insurances, taxes, cost of finance and profit)
Project ReportThe availability of a project report will be a good guide in cost management of a project at the construction stage. A project report is expected to be prepared in the final stage in project preparation. According to Raina (1993), the basic format of a project report should cover the items, in the order given below: Introductory report. Specifications. Design Data. Hydraulic and design calculations. Materials and resources. Estimate of quantities. Analysis of rates. Abstract of the estimate. Construction schedules. Drawings and plans. Sub-estimate for approaches Economic feasibility.
Essence of Cost Management at the Construction Stage
The essence of cost management of a bridge project at the construction stage is to ensure that adequate cost control measures are made using all methods of controlling the cost of the bridge within the limits of a predetermined sum, throughout the construction stage. Adequate cost management is achievable through the following, among others:
• Evolving performance baselines.• Re-measurement of quantities.• Progress measurement ‘earned value principle’.• Detailed cost and resource modeling facilities.• Intelligent resource rescheduling options.• Detailed network modeling facilities.
Chitkara (2011) postulated that performance is measured with respect to predetermined specified target or standard termed ‘Performance baselines’; these lines are devices used for measuring performance variations by comparing the originally planned performance with actual performance to determine the deviations from the planned path. The followings are some performance baselines and other parameters vital for cost management of a project at the construction/completion stages:Earned Value Analysis (EVA)This compares the value of work done with the value of the work that should have been done. EVA is often presented in the form of progress, productivity or S-curve diagrams.
Budgeted Cost of Work Scheduled (BCWS)This is the value of work that should have been done at a given point in time. This takes the work planned to have been done and the budget for each task, indicating the portion of the budget planned to have been used.
Budgeted Cost of Work Performed (BCWP)This is the value of the work done at a point in time. This takes the work that has been done and the budget for each task, indicating what portion of the budget ought to have been used to achieve it.
Actual Cost of Work Performed (ACWP)This is the actual cost of work done.
Productivity FactorThis is the ratio of the estimated man-hours to the actual man-hours.
Schedule Variance (SV)This is the value of the work done minus the value of the work that should have been done (BCWP – BCWS). A negative number implies that the work is behind schedule.Cost Variance (CV)This is the budgeted cost of the work done to date minus the actual cost of the work done to date (BCWP – ACWP). A negative number implies a current budget overrun.
Variance at CompletionThis is the budget (baseline) at completion (BAC) minus estimate at completion. A negative number implies that the project is over budget.
Schedule Performance Index This is attained by (BCWP/BCWS) x 100. Values under 100 indicate that the project is over budget or behind schedule.
Cost Performance Index This is attained by (BCWP/ACWP) x 100. Values under 100 indicate that the project is over budget.
Value of Work done Control
Bower and Merna (1995) postulated that the value of work done is not expenditure, although it, eventually equates to expenditure; it is often considered as the work in progress but is, most of the time, greater than the expenditure. There is normally a considerable time-lag between having a project ready for start-up and the final payment of invoices and retention when the project is completed in financial terms. The value of work done can be summarized as design and head office costs plus the value of materials delivered to site and the work done at site.
The techniques for an approximation of value of work done from month to month can be related to three major areas: Head office, materials deliveries to site and erection.
The activities carried out by the head office, usually: design, procurement and project supervision should be measured in man-hours. The work done measured in man-hours should be recorded on weekly basis and cumulatively.
Receipt notes of materials delivered to site can be valued, using information on the order, and a progressive total maintained. Materials are usually delivered to site against form orders; this makes order value(s) available. Materials delivered to site should be thoroughly inspected. Weighing bridge (if available) could be used for bulky materials and multiplied by an average price per kilogram calculated from the order(s).
Labour inputs on site should be recorded daily; where possible, labour inputs should be measured and recorded in man-hours. This is done in order to monitor performance against the budgeted man-hours.
The erection time should be measured in man-hours, especially in erection contracts. Erection man-hours exclusive of site supervision, for all contracts on site, should be recorded from week to week. Where evaluations of progress on site run late, erection man-hours worked are often valued on the basis of standards multiplied by an average rate per hour, applicable to the erection activity.
Conclusion
The record of measurement and cost management in civil engineering and by extension heavy engineering indicates the need for improvement. Many projects show inadequate measurements and massive cost and time over-runs. These are frequently caused by non-adherence to standard methods of measurements, underestimating and inadequate cost management.
The quantity surveyors with their knowledge base in measurement, cost estimating and management would fill the gap created by these inadequacies. Young quantity surveyors should make use of every opportunity, to be engaged on civil and heavy engineering projects.
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