JOURNAL OF THE AUSTRALIAN INSTITUTE OF STEEL CONSTRUCTION A.C.N. 000 973 839 STEEL CONSTRUCTION COSTING OF STEELWORK FROM FEASIBILITY THROUGH TO COMPLETION VOLUME 30 NUMBER 2 JUNE 1996 ISSN 0049-2205 Print Post Approved pp 255003/01614 $7.00 AISC MEMBERS… THE BEST IN STEEL FABRICATION AISC disseminates information on up-to-date steel design and fabrication technology, and this information flows to its detailer and fabricator members. When considering fabricated steelwork it makes sense to deal with those detailers and fabricators who share the institute’s resources. Their names, addresses and telephone numbers are listed below. While every effort has been made and all reasonable care taken to ensure the accuracy of the material contained herein the Authors, Editors and Publishers of this Publication shall not be held to be liable or responsible in any way whatsoever and expressly disclaim any liability or responsibility for any loss or damage costs or expenses howsoever incurred by any person whether the purchaser of this work or otherwise including but without in any way limiting any loss or damage costs or expenses incurred as a result of or in connection with the reliance whether whole or partial by any person as aforesaid upon any part of the contents of this publication. Should expert assistance be required, the services of a competent professional person should be sought. © AUSTRALIAN INSTITUTE OF STEEL CONSTRUCTION NEW SOUTH WALES T & S Bates Pty Ltd PO Box 308, Engadine NSW 2233 . . . . . (02) 520 6096 QUEENSLAND BDS Technical Services 80 Tribune Street, South Brisbane 4101 . (07) 3844 8093 G & D Drafting Pty Ltd PO Box 928, Cleveland 4163 . . . . . . . . (07) 3252 5124 QEI Pty Ltd 361-363 Montague Road, West End 4101 . . . . . . . . . . . . . . . . . . . (07) 3844 2772 Steelcad Drafting Pty Ltd 4/27 Birubi Street, Coorparoo 4151 . . . (07) 3847 3799 Steeltech Steel Detailers Pty Ltd 24 Curzon Street, Tennyson 4105 . . . . (07) 3848 6464 VICTORIA Bayside B W E Pty Ltd 7 Bowen Crescent, Melbourne 3004 . . (03) 9867 6066 Bayside Drafting (Aust) Pty Ltd Cnr Skye Road & Farrell Street, Frankston 3199 . . . . . . . . . . . . . . . . . . . (03) 9781 4011 BDS Technical Services Level 1, 240 Bay Street, Brighton 3186 . . . . . . . . . . . . . . . . . . . . (03) 9596 6500 WESTERN AUSTRALIA Perth Drafting Company (WA) 48 Kishorn Road, Applecross 6153 . . . . (09) 364 8288 Steelplan Drafting Services 15/885 Albany Highway, East Victoria Park 6101 . . . . . . . . . . . . . (09) 362 2599 For detailing of steelwork For fabricated steelwork See page 48 STEEL CONSTRUCTION VOLUME 30 NUMBER 2, JUNE 1996 1 AISC OFFICES SYDNEY Level 13, 99 Mount Street North Sydney NSW 2060 (P.O. Box 6366, North Sydney NSW 2059) Telephone (02) 9929 6666 Facsimile (02) 9955 5406 BRISBANE State Manager – Queensland Telephone (07) 3371 3633 MELBOURNE State Manager – Victoria Telephone (03) 9699 8138 PERTH State Manager – Western Australia Telephone (09) 367 0617 STEEL CONSTRUCTION is published quarterly by the Australian Institute of Steel Construction – a national body whose purpose is to promote the use of fabricated steel through engineering, research and the dissemination of knowledge. Its services, which are available free of charge to corporate members, include technical information and advice and a library which contains local and overseas publications. For details regarding AISC services, readers may contact the Institute’s offices: AISC CONTACTS ACT & SOUTHERN NSW Mr Robert Thompson Telephone (06) 281 1711 ILLAWARRA Mr Ken Wilyman Telephone (042) 28 4133 NEWCASTLE & NORTHERN NSW Mr José Zaragoza Telephone (02) 9929 6666 SOUTH AUSTRALIA Mr Les Nash Telephone (08) 302 3330 TASMANIA Mr Graham O’Byrne Telephone (003) 31 7044 CONTRIBUTIONS Contributions of original papers on steel design, research and allied technical matters are invited from readers of “Steel Construction’’, for publication in the journal. The editor also invites readers to submit letters, comments and discussions on papers appearing in “Steel Construction’’. Editor: Arun Syam EDITORIAL It has long been recognised that the costing of structural steelwork cannot be accurately determined by rates based on $/tonne, weight/square metre, etc – i.e. by weight concepts alone. The costs associated with various connection types, materials procurement and the value adding processes of detailing, fabrication, coating, transportation and erection are essentially process dependent. Current design optimization techniques generally utilise the steel weight criterion which does not necessarily produce minimum cost solutions. However, rational methods of costing have not been readily available. The paper contained in this issue of Steel Construction entitled “Costing of Steelwork from Feasibility through to Completion” considers a new method of costing steelwork. The method examines costs associated with each process and breaks it up into costs related to steel supply, fabrication, surface treatment and erection. The paper also illustrates the methodology by several case studies. As the new costing method is published in the journal for further industry comment, the authors would welcome any feedback on its details and application. Additionally, readers should note that the regular Steel Construction “Current Cost Indicators” – which was generally based on a $/tonne method – has been withdrawn. This has been due to various reasons – the primary one being its inconsistency with the preferred new costing method. AISC MEMBERS… THE BEST IN STEEL FABRICATION AISC disseminates information on up-to-date steel design and fabrication technology, and this information flows to its detailer and fabricator members. When considering fabricated steelwork it makes sense to deal with those detailers and fabricators who share the institute’s resources. Their names, addresses and telephone numbers are listed below. While every effort has been made and all reasonable care taken to ensure the accuracy of the material contained herein the Authors, Editors and Publishers of this Publication shall not be held to be liable or responsible in any way whatsoever and expressly disclaim any liability or responsibility for any loss or damage costs or expenses howsoever incurred by any person whether the purchaser of this work or otherwise including but without in any way limiting any loss or damage costs or expenses incurred as a result of or in connection with the reliance whether whole or partial by any person as aforesaid upon any part of the contents of this publication. Should expert assistance be required, the services of a competent professional person should be sought. © AUSTRALIAN INSTITUTE OF STEEL CONSTRUCTION NEW SOUTH WALES T & S Bates Pty Ltd PO Box 308, Engadine NSW 2233 . . . . . (02) 520 6096 QUEENSLAND BDS Technical Services 80 Tribune Street, South Brisbane 4101 . (07) 3844 8093 G & D Drafting Pty Ltd PO Box 928, Cleveland 4163 . . . . . . . . (07) 3252 5124 QEI Pty Ltd 361-363 Montague Road, West End 4101 . . . . . . . . . . . . . . . . . . . (07) 3844 2772 Steelcad Drafting Pty Ltd 4/27 Birubi Street, Coorparoo 4151 . . . (07) 3847 3799 Steeltech Steel Detailers Pty Ltd 24 Curzon Street, Tennyson 4105 . . . . (07) 3848 6464 VICTORIA Bayside B W E Pty Ltd 7 Bowen Crescent, Melbourne 3004 . . (03) 9867 6066 Bayside Drafting (Aust) Pty Ltd Cnr Skye Road & Farrell Street, Frankston 3199 . . . . . . . . . . . . . . . . . . . (03) 9781 4011 BDS Technical Services Level 1, 240 Bay Street, Brighton 3186 . . . . . . . . . . . . . . . . . . . . (03) 9596 6500 WESTERN AUSTRALIA Perth Drafting Company (WA) 48 Kishorn Road, Applecross 6153 . . . . (09) 364 8288 Steelplan Drafting Services 15/885 Albany Highway, East Victoria Park 6101 . . . . . . . . . . . . . (09) 362 2599 For detailing of steelwork For fabricated steelwork See page 48 STEEL CONSTRUCTION VOLUME 30 NUMBER 2, JUNE 19962 1. INTRODUCTION A considerable amount of effort is devoted during the design process to optimizing the design to achieve a min- imum cost solution. The measure traditionally used to judge the economy of the design is the quantity of steel in the structure expressed as a weight per square metre of floor area or per cubic metre of cubic content (Hart Henn & Sontag (1)). Therefore, the optimization of a design has meant the minimization of the quantity of material in a pro- ject. This has permeated all facets of design, construction and research. For steel structures, the current method of costing steelwork on the basis of a rate per tonne has lead to this concentration on minimum mass solutions. Yet Girardier (2) indicates that the material cost represents only 40% of the total cost of the steel frame. The remain- ing 60% of the cost represents the value added in fabrica- tion and erection which has been very difficult to accurately quantify. This latter component has often been neglected in design. For example, the cost of stiffening a penetration can add considerably to the cost a beam, yet it is often not considered worthwhile to carry out a design to determine the level of stiffening required. By compari- son, a considerable time is typically spent minimizing the size of the member. Various proposals (Australian Institute of Steel Construction (3), Hogan and Firkins (4)) have been made to remedy this situation and some worthwhile general principles have been developed. These have included advice such as: weld in the fabrication shop, bolt on site; adopt simply supported connections not continuous. Whilst these qualitative principles will generally apply, they do not allow the particular situation to be adequate- ly investigated. There has also been some industry skep- ticism on whether the benefits of adopting good design principles were being passed on to the client in the form of lower prices. In fact, it was frequently perceived that good design was costing more, as the design was often heavier and hence on a rate per tonne basis it would cost more. Firkins and Hemphill (5) advised on work hours per tonne for various types of work and whilst this was a refinement, it translated into a rate per tonne. It was an average rate and did not allow details to be costed with sufficient accuracy to allow comparisons to be undertak- en. This method has the additional disadvantage that it is very dependent on the experience of the estimator in the particular type of work. To help give a better understanding of the total cost of steelwork, Watson and Buchhorn (6) developed concepts for costing steelwork in which components of the cost were taken into account. The concepts proposed were similar to those practices adopted by the professional fabricators. The method was further developed (Watson, Dallas & Main (7); Main, Watson & Dallas (8) and Watson & Dallas (9)) into a practical and rational method of costing steelwork. During this period extensive consultations were undertak- en with all sections of the Australian construction industry which lead to the method being refined and extended to cover most types of steel construction. The steel construc- tion industry has been very supportive of these develop- ments as the system reduces the contractual risks to the fabricator and also reduces the cost of tendering by pro- viding a format consistent with the fabricator’s method of estimating. Tizani, Davies, Nethercot and Smith (10) have been devel- oping knowledge based engineering systems to carry out comparative costing on different space frame systems. Their approach is similar to that discussed in this paper. This paper explains the method and uses case studies to illustrate the insight that can be achieved into factors influ- encing costs. Extensive tables of indicative unit rates are given so that most structures can be costed. The applica- tion of the method at various stages of the design and con- struction process is demonstrated with particular attention being given to extending the method to cover early stages of design. Indicative sizes and costing are given for portal frame industrial buildings, carpark, office and retail floors to assist with costing at the early stages of design. The pro- posed method presented has not yet been fully extended to cover all plate structures such as bins and silos. However the principles can readily be applied to such structures. 2. THE CURRENT METHOD When pricing a job, fabricators determine the cost of the supply of materials, the number of hours involved in fabri- cating steelwork, and the costs for surface treatment and erection.These costs are then summed and divided by the total number of tonnes to determine a rate per tonne to be included in the tender documents.Therefore the rates rep- resent an average across the total job and do not prove very useful in determining the cost of variations or refining designs. The format of the breakup is guided by the Australian Standard AS1181- 1982 (11) for civil engineer- COSTING OF STEELWORK FROM FEASIBILITY THROUGH TO COMPLETION K.B. Watson, S. Dallas and N. van der Kreek BHP Structural Steel Development Group T. Main Trevor Main & Associates STEEL CONSTRUCTION VOLUME 30 NUMBER 2, JUNE 1996 3 ing projects and the Institute of Quantity Surveyors and Master Builders’ – Construction and Housing Association’s (12) Standard Method of Measurement (SMM5) for building projects. Table 1 shows that there is a great variation in cost of steelwork on a dollars per tonne basis. The variation reflects the complexity of the work to fabricate and erect.To overcome this wide spread, rates have been developed and published (Cordell (13), Rawlinsons (14)) for various types of work. Poulos (15) investigated the costs of three different portal frame designs for a 2,000 square metre building with a span of 30 metres. The results are summarised in Table 2 and show a 36% variation in tonnage rates over the three designs. This illustrates that even for standard structures the current method cannot give accurate and reliable cost- ing of projects. Whilst the ‘conservative’ design increased the tonnage by 12% over that required for the ‘good’ design, the total cost of the frames increased by only 6%. This was because only the steel supply component of the cost increased as there was no difference in the cost of the shop drawings, fabrication, transport and erection. However, for the skinny design a corresponding decrease in the mass of steel from the ‘good’ design increased the cost of the frame by 15%. This increase was caused by more complicated knee connections, additional fly bracing and additional costs in erecting flimsy members. Therefore the current method, which leads to minimising weight can result in more costly designs. 3. PROPOSED NEW METHOD OF COSTING As accurate costing is one of the essential features neces- sary to design and construct economical structures, it was decided to develop a rational costing method which will overcome these deficiencies.The goals of the new method are to: • give a more reliable and accurate method • provide a continuity of approach from initial project costing through to fabricator’s detailed costing • provide a clearer focus on the elements that will have a significant effect on the final cost • allow reliable determination of cost of contract varia- tions • provide a methodology which is simple to understand. In order to achieve these goals, the costs are divided into four components: steel supply, fabrication, surface treat- ment and erection. Costs represent rates received from fabricators and as such, they do not include the builder’s margin. The indicative costs given in Appendix A are applicable for projects where the steelwork cost (supply, fabrication and erection) is greater than $150,000.The cur- rent hourly labour rate adopted for the tables is $40.00. 3.1 Steel Supply Steel supply covers the supply of all materials including hot rolled, welded, cold formed and tubular sections, plate, as well as items such as bolts and shear studs. (Refer Appendix A1 for tables.) Sections are costed on a rate per metre basis. This brings the costing of hot rolled sections into line with cold formed sections, such as purlins and tubular sections, which have been traditionally been sold on a per metre basis. Another advantage of this method is that it allows a very quick com- parison to be undertaken on different sections capable of carrying the same load. Plate is costed on a rate per square metre basis.This gives a more realistic measure than dollars per tonne and allows for any changes in the cost of steel with thickness to be highlighted as shown in Figure 1. Wastage has not been allowed for in the rates given as it can be minimised in the design process. For instance, Design Description Frame Mass Cost $ / tonne (tonnes) ($) ‘Good’ Design 20.2 45,646 2,260 ‘Conservative’ Design 22.6 48,530 2,147 ‘Skinny’ Design 18.0 52,679 2,927 Table 2. Comparison of costs for different designs for 2,000 square metre portal frame building (span 30m). Item Cost ($) / tonne Variation (times lowest cost) Steel supply 900 - 1,300 1.4 Shop detailing 50 - 500 10.0 Fabrication 200 - 2,000 10.0 Surface treatment 0 - 750 ∞ Transport to site 50 - 200 4.0 Erection 150 - 700 4.7 TOTAL 1,350 - 5,450 4.0 Table 1. Typical range of tonnage rates. there is often the opportunity to eliminate wastage, or at least minimise it, by designing with standard lengths in mind (Refer Appendix B and BHP Steel (16) for details of standard lengths), or by providing sufficient time in the pro- ject programme for the steel to be supplied cut to the spec- ified length by the manufacturer. Wastage is typically 2-5% for a project. By combining the requirements for a number of smaller projects the wastage level can be minimised to similar levels to that of larger projects. 3.2 Fabrication 3.2.1 Introduction Fabrication covers each activity after the delivery of steel to the fabricator to the delivery of steel to site. It includes: shop detailing; fabrication of end connections, items along a member, compound members; and transport. Surface treatment is covered as a separate item in Section 3.3. It is proposed that all costing be activity based. The time required to undertake each activity is therefore used. This has the advantage that it is relatively constant across Australia and is not subject to significant fluctuations with the changing economic times. With relatively expensive machines, like beam lines, the cost has been converted into equivalent work hours to include capitalised costs and hence simplify the method. Consumables, minor equip- ment, overheads and profits are included in the hourly rate. The hourly rate is readily obtainable and allows costs to be updated to reflect the local economic situation. It was found that a high level of accuracy can generally be achieved by providing rates for three different section weight ranges. The fabricator will cost the job in finer detail when tender- ing on a project. Fabrication rates are given in Appendix A2. 3.2.2 End Connections It is proposed that all the hours associated with a connection are allocated to the supported member. Appendix A2.1 gives tables of rates for commonly used standard connec- tions. 3.2.3 Work Along a Member This covers work along a member which is not associated with connection to another member. Examples include purlin and other cleats, penetrations, architectural connec- tions. Refer to Appendix A2.2 for rates. 3.2.4 Compound Members Compound members are members built up from individual components and include three plate members, trough and box girders, box columns, trusses, vierendeel trusses and battened columns. These members form two different cat- egories: • Members whose costs of fabrication are related to their length. Examples of these include three plate members and box columns. The cost of fabricating these mem- bers is given as a rate per metre.Table A2.2.4 gives the rates for fabricating a three plate girder. • The costs of fabricating trusses, vierendeel trusses and battened columns are dependent largely on the costs associated with each joint. Examples of fabrica- tion costs for different types of trusses are given in Table A2.2.5. 3.2.5 Other Fabrication Items It is not possible to fully cover every detail in tables such as given in Appendices A2.1 and A2.2.To assist in developing costs for details not covered, some elemental costs are STEEL CONSTRUCTION VOLUME 30 NUMBER 2, JUNE 19964 Fig 1. Steel Supply Plate Pricing STEEL CONSTRUCTION VOLUME 30 NUMBER 2, JUNE 1996 5 included in Appendix A2.3. These costs may need to be supplemented with advice from fabricators. The costs given in Appendix A2.1 and A2.2 are complete costs for the fabrication of the item and hence already include the costs given in Appendix A2.3. 3.2.6 Shop Detailing Watson et. al. (7) referenced the cost of shop drawings back to the number of hours of fabrication. The ratio varied from 1 hour of shop detailing for every 4 hours of fabrica- tion for portal frame work, to parity for complex work involv- ing significant variations. Main et. al. (8) gave guidance on the number of hours required to draw marking plans, individual members, com- ponents and carry out checking. The estimator is then required to determine the number of drawings. The time to prepare shop drawings is dependent on the quality of the contract drawings, the complexity of the pro- ject and the amount of repetition.There has been a decline in the quality of contract drawings as fee pressure has intensified. This is usually a false economy, as the shop detailer must fill in the gaps in information, and this results in significantly increasing the costs of shop detailing. Where members are identical, the costs of detailing are significantly reduced as the member is only drawn once. Minor differences in details add to the cost, as they must be noted on drawings or the members redrawn. When sever- al people are working on a project, there should be com- mon detailing across the whole project, otherwise members will be required to be redrawn needlessly. Due to difficulties in determining the number of identical and similar members early in the design process, it is rec- ommended that a method of relating the cost of detailing to the cost of fabrication be used at this stage (refer Table A2.4.1). As the design is finalised, the estimate can be refined if it is based on the number of shop drawings (refer Table A2.4.2). 3.2.7 Transport The cost of transport is directly related to the number of truck loads of steel, the size of the loads and time taken to load, transport and unload the steel. Hence the cost is related to both the weight and volume of steel and to a lesser extent the distance from the site. Table A2.5.1 gives the rate per member to transport beam and stick type steelwork. The total typical travel time for a city delivery is 9 hours per load which is composed of the following components: time from depot to fabrication shop (1.0 hour); time to load steel- work on truck ( 2.5 hours); fabrication shop to site (1.5 hours); waiting time at site and the time to unload steelwork (3 hours); travel time back to depot (1 hour). This highlights the significant time and subsequent cost savings that could be made by palletising fabricated steelwork. Transport costs for other types of work can be calculated using the above principles. When transporting bulky items such as three dimensional trusses, the volume will deter- mine the number of items that can be carried on a truck. If the steel is galvanised or painted at an external shop, the cost of transport is almost doubled as the steel is trans- ported twice, once to the galvanisers or paint shop and then to site. It is recommended that this additional cost be included in the surface treatment cost. 3.3 Surface Treatment Surface treatment covers all forms of treatment to the steel and includes painting, galvanising, fire spray, intumescent paint and fire rated board systems. A rate per square metre of applied treatment has been adopted as the appropriate measurement. Differences in handling, thickness of zinc in galvanising and thickness of fire spray due to changing surface to mass ratio have been allowed for by giving rates for three different mass per metre categories as shown in Appendix A3. For the fire rated board systems, the project- ed area will generally be applicable. Appendix C gives the surface areas for standard sections which makes the pro- posed method very simple to apply. 3.4 Erection The key determinant in the cost of erecting steelwork is the number of lifts that are required. Once the crane size is determined based on the dual requirements of lifting radius and mass of component, it costs virtually the same to lift a very light member as a heavy member. The cost of erect- ing bigger sections has been increased to allow for the extra time for the end connections and to plumb the steel- work. Appendix A4 gives typical costs per member for por- tal frames and multi-storey buildings. For other types of projects it is recommended that the costs be derived using the same methodology. This is illus- trated by the bridge example in section 3.5.2. 4. CASE STUDIES 4.1 Case Study No. 1 – Portal Frame The costing of an internal bay of a 2000 square metre warehouse with portal frames at 9 metre centres and 6 metre eaves is given in Appendix D1. This shows that approximately 60% of the cost of the building is in the purlins and sheeting. However, the time spent in optimising designs of portal frames has generally been on minimising the tonnage in the frame which represents only 20% of the cost of the building. As was shown in section 3, this effort can be counter productive and lead to more expensive designs. An alkyd primer (red oxide zinc phosphate) paint system was chosen as providing adequate corrosion protection. This paint system is usually applied in the fabrication shop. However, if an inorganic zinc silicate system was adopted, the steel would normally have to be transported to a spe- cialist contractor to be grit blasted and painted. The total cost of painting would have increased four fold with the use of inorganic zinc silicate. It is normal practice for the fabricator to be responsible for the supply of cranes on industrial projects and therefore this has been allowed for in the costing. This costing method allows the determination of the most economical spacings of the portal frames and purlins. 4.2 Case Study No. 2 – Multi Storey Building A ten level office building with a floor plate of 1000 square metres net per floor was chosen to investigate the costing method (refer Figure 2). A conventional layout with beams spanning from the perimeter to the core was prepared (refer Figure D2.1). A 120mm deep slab on 1.0mm Bondek II spanned 2.8 metres between the steel beams. The floor structure was required to accommodate a major air condi- tioning (A/C) duct around the reinforced concrete core. A steel depth limit of 300mm was adopted in this area to maintain a reasonable plenum height (the height from underside of ceiling to the top of slab above). Also, the A/C duct layout and flexibility requirements indicated web pen- etrations at third points in the typical secondary beams B1 and B7. Other internal beams were specified to have small circular penetrations at third points for services. The floor beams were designed in accordance with the soon to be released composite beam standard AS2327.1-1996 (17). Beams were cambered for their self weight and the con- crete slab weight. The initial design, referred to as Design A, had an overall steel beam intensity of 31kg/sq.m. This scheme involved stiffened web penetrations in B1 and B7 which were 460UB67.1 beams. Alternatively, adopting 530UB82.0 beams in these locations eliminated the need for stiffening at the web penetrations. This scheme had a beam steel intensity of 35kg/sq.m and is referred to as Design B. Appendix D2 gives a full costing of beams for Design A and the varied beams in Design B, using the proposed method of costing. The results are summarised in Table 3. When costing according to the proposed method, the steel frame cost of Design B is slightly lower even though it is heavier than Design A. However traditional methods of costing based on a constant dollars per tonne rate would have quickly ruled out Design B, as it was heavier. For Design A, the stiffener supply and fabrication costs at the penetrations totalled $190 per penetration compared to $32 for Design B with its unstiffened penetrations. When the extra beam supply and firespray costs associated with a 530UB82.0 were also included, a similar overall cost resulted. Steel cost includes supply, shop detailing, fabri- cation, fire-spray, transport and erection of structural steelwork. The fire spray cost for both schemes represented about 20% of the total steel-frame cost. Bennetts and Thomas (18) showed that on the 40 storey, 140 William Street, office building in Melbourne that if a reliable fire sprinkler system was installed and the passive fire protection removed, the building would be safer than a building meet- ing the building regulations. The fire spray on this building was subsequently not reapplied during the refurbishment. The shop detailing was costed by estimating the number of drawings. It was decided that each beam type would be kept identical throughout the 10 floors. Consequently, the shop detailing cost represented less than 1% of the total steelwork cost. However if changes were made such as having different end connection on some members, chang- ing penetration sizes throughout the floor and between floors, the cost of shop details could increase to about 5% of the total steel cost. The plenum height is influenced by a variety of factors such as the depth and layout of the mechanical services, the depth of the beam/slab at beam notches and the depth of the lights. Even though some beams were increased in depth in Design B, it would not generally require a greater plenum height than Design A.Therefore facade costs were not included in the cost comparison. Also, crane costs have not been included since for this type of project the crane is normally provided by the builder. 4.3 Case Study No 3. – 34.5 m span Bridge The structures used in the previous examples have significant repetition and similarity between projects and hence industry rates could be developed. This comment particularly applies to site activities. Accordingly for more complex projects, or for projects with less repetition, the published rates may need to be supplemented with rates developed from first principles. A simply supported skewed bridge spanning 34.5 metres is used to demon- strate the application of the method. STEEL CONSTRUCTION VOLUME 30 NUMBER 2, JUNE 19966 Item Design A Design B Steel Frame Intensity 31 kg/sq m 35 kg/sq m Steel Floor Frame Cost * $86.60 /sq m $85.50 /sq m * Costs exclude columns, steel decking and the reinforced concrete slab, which would be similar for the two layouts. Table 3. Cost Comparison of Designs. Fig 2. Floor Layout STEEL CONSTRUCTION VOLUME 30 NUMBER 2, JUNE 1996 7 4.3.1 Bridge Design The bridge is shown in Appendix D3 and is skewed at 15° to the road alignment. The bridge spans 34.5 metres with a width of 12.6 metres and consists of four composite plate I-beams, each weighing approximately 25 tonnes, at a spacing of 3.5 metres. Grade 350 steel has been adopted for the top flange and as the bridge is designed in accor- dance with Victorian conditions, Grade 350L15 has been used for the bottom flange. The web is Grade 250. The plate lengths were chosen to minimise the number of splices within the length of the beam. The concrete deck is composed of precast formwork acting compositely with the insitu concrete. The surface treatment specified for the project was Class 2.5 blast together with 75µm of inorganic zinc silicate. This has been found to provide a very good life as well as being an economical solution. 4.3.2 Costing Of The Bridge Appendix D3 shows the estimated costs of the supply, fab- rication, surface treatment and erection of the beams, intermediate and abutment cross frames. (a) Steel Supply The areas of plate and the lengths of sections were calcu- lated and the appropriate rates applied. During this process the various length, width and thickness combinations of plates were investigated to minimise the number of welded splices and ensure the required combination was available (Refer Appendix B). For bridges, it is usually necessary to order the required combination rather than rely on standard plates which have a maximum length of 12 metres and are mainly available in Grade 250. A smaller range of Grade 350 standard plate is also stocked by distributors. A 5% wastage factor was allowed for trimming the plates and for the waste involved in profiling the web to provide the specified camber. This could have been refined by investi- gating in more detail the exact size of plates required. (b) Fabrication The fabrication costs of the beams and cross frames were quickly and simply obtained from the relevant tables. The mass per metre of the beam was greater than given in the table for the fabrication of gussets (or stiffeners). After con- sultation with some fabricators, it was agreed that the high- est rate in the table would be appropriate. Bridge design drawings generally contain sufficient infor- mation so that shop drawings are not required. The transport of the 35 metre long beams required special consideration as they were significantly over length and would therefore require pilot vehicles and semi trailers with steerable rear bogies. A specialist transport company was contacted and it was determined that it would be feasible and most economical to transport two beams and the cross bracing per truck. It was also determined that one load would be scheduled per day. A budget price was then developed and used as the basis of costing. (c) Surface Treatment The surface areas were readily determined and the appro- priate rates for inorganic zinc silicate applied. (d) Erection A layout of the site was prepared and it was determined that it was necessary to lift 25 tonnes at a radius of 20 metres. A number of crane hire companies were then con- tacted to determine suitable mobile cranes. A 150 tonne crawler crane was required to enable a single crane lift. For such large cranes the mobilisation and demobilisation costs form a large component of the total cost of the erec- tion where there is a small number of members to be lifted into place. It was determined that the crane would be required to be on site for a total of a week. A rigging crew of 3 was allowed. (e) Accuracy of estimate To confirm the accuracy of the method and rates, a num- ber of fabricators were asked to price the bridge. Detailed pricing by the fabricators was found to be in close agree- ment with those given in Appendix D3. 4.3.3 Comparison With Traditional Design This method allows the designer to assess the impact of different structural arrangements to be determined with accuracy. For example the beam spacing of 3.5 metres is compared with the traditional spacing of steel beams of 1.8 to 2.5 metres (Rapattoni (19)). The reduced spacing increased the number of beams from 4 to 6. Haywood (20) indicates the steel quantity would be slight- ly increased with the traditional beam spacing. Appendix D3 illustrates that the fabrication, surface treatment and time related erection cost are proportional to the number of beams. Therefore the cost of these items would increase by approximately 50%. This would increase overall cost of the steelwork for the bridge by about 20%. 5. APPLICATION OF METHOD AT DIFFERENT STAGES OF PROJECT 5.1 Stage 1 – Pre-design Costing At this stage of a project the information is often very sketchy and the aim of the study is to determine whether the project is worth proceeding with. Therefore the inputs are the variables affecting the cost and revenue from the project. For example on an office development the key variable is the amount of floor space. Hence it is impor- tant to have reliable costs per square metre of office space. These costs can be derived from previous projects using the methodology presented in Section 3. A database from previous similar projects would allow this information to be built up. Perara and Bennett (21) reviewed methods of modeling data from previous projects to predict the cost of the project. The models can be categorised as three types: Parametric Cost Models, Regression Models, and Probabilistic Models. There are also public sources of such information pub- lished on a regular basis such as Cordells(13) and Rawlinsons(14). A number of pre-design rates for industrial buildings, office and retail floors are given in Appendix E.The order of accu- racy of estimate at this time would be ±20%. [...]... Steelwork Steel Construction Vol 24 No 2, Australian Institute of Steel Construction 6 WATSON, K.B AND D.P BUCHHORN (1992) “A new approach to costing structural steelwork Proceedings of the Third Pacific Structural Steel Conference, Japanese Society of Steel Construction pp 437-444 7 WATSON, K.B., S DALLAS AND T MAIN (1994) Costing of Structural Steelwork – The Need for a New Approach” Preprints Of Papers... Institution of Engineers, Australia Vol 2 pp 1039-1046 8 MAIN T., K.B WATSON AND S DALLAS (1995) “A Rational Approach to Costing Steelwork Construction Economics – The Essential Management Tool The Australian Institute of Building Surveyors 9 WATSON, K.B AND S DALLAS (1995) “New Method of Costing Steelwork – The Way to Economical Structures” Structural Steel: PSSC ’95, 4th Pacific Structural Steel Conference... square metre of treatment • Erection - cost per lift STEEL CONSTRUCTION VOLUME 30 NUMBER 2, JUNE 1996 The method has been shown to be simple to apply at all stages of a project from pre-design, design, tendering through to contract administration It has proven to provide a valuable tool in the economical design and construction of steel structures 9 ACKNOWLEDGEMENTS The Authors would like to thank those... systems can be relatively easily changed to accommodate the new method of costing One interesting development is the linking of design and drafting systems into costing systems There are a number of instances where the Computer Aided Drafting System has been linked to the costing system This saves a considerable amount of time, but probably more importantly the number of errors 8 CONCLUSIONS A rational new... Institute of Steel Construction (1992) “Economical Structural Steelwork (Third Edition) 4 HOGAN,T.J AND A FIRKINS (1986) “Economical Design and Construction of Medium Rise Commercial Buildings using Structural Steel Proceedings of the Pacific Structural Steel Conference New Zealand Heavy Engineering Reasearch Association Vol 1 pp 243-263 5 FIRKINS, A AND R HEMPHILL (1990) “Fabrication Cost of Structural Steelwork ... been used successfully on a number of projects to help resolve disputes on variations This saves a considerable amount of time and therefore costs, in administering a contract 8 6 STANDARD METHOD OF MEASUREMENTS The Victorian Fabricators Sub-Committee of the Australian Institute of Steel Construction (27) have developed a draft revision for amending the SMM5 (12) to incorporate the new method This... been shown to give improved reliability and accuracy in costing steelwork It provides a common language that can be used by all participants at every stage of the design and construction of the structure The new approach is based on dividing the costing exercise into four components: • Steel supply - cost per metre for sections - cost per square metre for plate • Fabrication - cost per item of work •... Beams” Steel Construction Vol 29 No 4, Australian Institute of Steel Construction 25 WOOLCOCK, S.T., S KITIPORNCHAI, M.A BRADFORD (1993) “Limit State Design of Portal Frame Buildings.” 2nd Edition Australian Institute of Steel Construction 26 KITIPORNCHAI, S., L.W BLINCO, S.E GRUMMIT (1991) “Portal Frame Design Charts.” First Edition Australian Institute of Steel Construction 27 AUSTRALIAN INSTITUTE OF STEEL. .. 2 - 5 % 2) The base grade of hot rolled steel and welded sections is readily available ex-stock from distributors Higher grade steel must be specifically ordered (typical lead time – 8 weeks) and is subject to minimum order quantities For standard lengths and widths refer to Appendix B Subject to minimum order quantities and lead times, steel may be ordered to a specific length This can be useful when... (kg/m) Welded to Slotted Gussets Section mass Hours $ (kg/m) 2.0 5.1 80 204 < 60.5 60.6 to 160 Diagram Comments Equal Angles Bolted to Gussets Hours $ 0.9 1.3 1.8 36 52 72 < 30 30.1 to 60.5 60.6 to 120 Diagram Cut bracing member & Gusset CPBW web to gusset & CFW flanges to gusset CFW gusset to other members Comments Cut bracing member & Gusset Drill/Punch holes CFW gusset to other members STEEL CONSTRUCTION . JOURNAL OF THE AUSTRALIAN INSTITUTE OF STEEL CONSTRUCTION A .C. N. 000 973 839 STEEL CONSTRUCTION COSTING OF STEELWORK FROM FEASIBILITY THROUGH TO COMPLETION VOLUME 30 NUMBER 2 JUNE 1996 ISSN. invited from readers of Steel Construction’’, for publication in the journal. The editor also invites readers to submit letters, comments and discussions on papers appearing in Steel Construction’’. Editor:. For steel structures, the current method of costing steelwork on the basis of a rate per tonne has lead to this concentration on minimum mass solutions. Yet Girardier (2) indicates that the material