Transcription

How to Estimate the Cost of Different Structural Beam and Column Connections(Comparison)CPE Candidate No. 0115808July 07, 20151 Page

TABLE OF CONTENTS:Section 1: Introduction . . p.3Section 2: Types and Methods of Measurement . p. 4Section 3: Special Factors – Effects on Takeoff and Pricing . p. 5Section 4: Overview of Labor, Material, Equipment, Indirect Costs and Mark-Up . p. 6Section 5: Special Risk Considerations . . . p. 7Section 6: Ratios and Analysis – Metrics and Review for proper QA/QC . . p. 8Section 7: Miscellaneous Pertinent Information. . . .p. 8Section 8: Sample Drawings, Schedules and Sections . . . p. 9Section 9: Sample Estimate . p. 12Section 10: Glossary . . p. 15Section 11: References . . p. 152 Page

SECTION 1: INTRODUCTION:The structural component of a project is probably the most straight forward element to estimate. It is usually themost advanced during the design stages which paints the estimators a good ‘picture’ of the structural design even atthe early stages. The main structural members are defined early and are easily quantified but, more often than not,the structural connections are developed at later stages so estimators tend do just capture the cost for the connectionsin allowances based on a percentage of the total steel weight or gross square footage (GFA) of the project cost. Thisapproach is widely accepted when estimating new-build structures, since the structural connection costs are only afraction of the overall cost and can easily be covered as an allowance, based on the estimator’s judgment. Structuralretrofit projects are different. The structural connections represent a higher cost due to lower productivity rates andhigher difficulty of unforeseen challenges when installing in the field. Most steel components are field fabricated tofit, which add to the difficulty of the project.The main intention of this technical paper is to provide the reader a general understanding of different structuralbeam and column steel connections and understanding the potential impacts to a structural estimate. This will helpan estimator weigh the cost impact of the structural connections so the allowances applied are rather more‘educated’ than just a guess.MAIN CSI DIVISION:Division 03000 – ConcreteDivision 05000 – MetalsCSI SUBDIVISION:Subdivision 03100 – Concrete Forming and AccessoriesSubdivision 05100 – Structural Metal Framing3 Page

BRIEF DESCRIPTION:The author will discuss different types of steel connections by providing sample plans and details of these elements.Since there are numerous types of steel connections that have been engineered through the years, only thecommonly used are going to be discussed in this paper. The plans and section details will be used to perform thequantity takeoffs for the necessary tasks to develop the direct and indirect costs of the connections. Productivityrates are factored into the Labor costs due to the possible challenges whether in a new-build situation or a retrofitcondition. The estimator will need to assess whether a project can be considered ‘production work’, since this willaffect both material and labor productivity rates. Sample takeoffs and cost estimates will be provided to illustratethese. This paper is presented from a cost consultant’s point of view as opposed to a contractor’s or a materialsupplier’s. The estimate will be prepared as a general contractor bid, which will include the ‘General Contractor’s(GC)’ mark-ups. The estimates anticipate that the GC will hire a subcontractor to perform the tasks. The estimateswill show detailed breakdown of the tasks and quantities for the connections costs. Unit rates are then provided forthe quantities and extended for the total cost. Once the total cost for each task is determined, these are totaled as thetotal subcontractor cost, which then is marked up by the general contractor mark-ups. The total cost of theseconnections is then backed into the weight of the total steel as a percentage or to the GFA as a square foot cost.SECTION 2: TYPES AND METHODS OF MEASUREMENT:Quantifying structural beam and column connections involve measuring the components in SF(square feet),LBS(pounds) or TONS. Welds and cuts are measured in LF(linear feet). Bolts and anchors are counted in EA.(each).The connections will have typical detail drawings or section plans, showing the profiles and dimensions for eachtype of connection. The number of each connection type can then be counted on the floor framing plans, often usingdifferent symbols to represent each type of connection. Steel components are usually measured in SF and LF but canbe easily converted to LBS by referencing the steel properties of the members in any of the widely availablepublished materials. To use these references, the member sizes or sections have to be available. Wide Flanges (WF),I-shaped, H-shaped and channels designate the weight in the sizing such as W12x16, S8x23, HP8x37 and C10x30,4 Page

where 16, 23, 37 and 30’ represent the weights in lbs. For channels, angles and for hollow steel sections (HSS), thesizes will need to be referred to a steel table to determine the weights. An angle with size L4x4x1/2 has a weight of12.8 lbs per linear foot. A tubesteel with a size of HSS6x6x1/2 has a weight of 35.24 lbs. per linear foot. Plates areusually measured by the area but more importantly, the thickness has to be known to determine the weight. A platewith the thickness of 1/2” and 3/8” are 20.42 lbs. and 15.31 lbs, respectively.SECTION 3: SPECIAL FACTORS – EFFECTS ON TAKEOFF AND PRICING:The first thing to consider is whether the project is new-build or retrofit. Structural retrofit jobs require much morelabor to install primarily because of the onsite preparation for the connections to be installed. Unlike new-buildprojects where the steel can be prepared in the shop, retrofit jobs require preparation for the existing structuralmembers to be performed in place. Drilling and cutting are necessary to install new member to existing structure.Most of the steel members, if not all, are fabricated onsite to fit actual conditions which contribute to the difficultyand duration of the task.Project size is always a factor to consider for all projects. A larger project simply allows the contractor to spread theoverhead costs more effectively over the scope of work, including mobilization and demobilization costs, whichresult smaller unit costs. The contractor can offer lower profit mark-ups with larger projects since this will yieldhigher profit margins based on the larger direct costs. Installing structural connections requires the use of equipmentand specialty labor. The same economies of scale principle apply to equipment rentals. Lower rates are offered toequipment that are rented for longer periods of time. These lower rates then translate to the cost of installing thestructural connections. Specialty labor such as a welder usually have half-day or one day minimums set, regardless ifthe actual work takes an hour or a day. This also flows over to the structural connection cost.Workflow is another factor to consider. If workers can work continuously without have to demobilize and thenremobilize for the next task, this helps lower the construction cost. Phased construction is more expensive sincemultiple mob and demob costs need to be considered. Labor efficiency has to be optimized to yield lowest rates.The commonly used materials for structural members are steel, concrete and timber and they can be interconnectedto one another through different connections. Most of these connections are made of steel. These connections are5 Page

engineered and are unique for each project. So determining the type of structure can affect the type of connectionsbeing used in a project.The steel material and finish are other factors that can affect the cost. The commonly used steel material is hot-rolledor cold formed carbon steel, but some projects require stainless steel which is substantially heavier and moreexpensive than carbon steel. Some projects that have some exposed steel members may require the steel to be‘Architecturally Exposed Structural Steel’ (AESS). AESS is more expensive because the steel is fabricated as astructural and architectural element at the same time. The finish of the steel is also a factor. Most projects require thesteel to be primed and painted, but projects that are in corrosive environments, require the steel to have protectivecoatings such as hot-dipped galvanizing, PVC wrapping or epoxy coating.Another important factor to consider is whether a system is a proprietary system like “Sideplate”. These systems areengineered for faster installation by the system developer and require licensing fees for the utilization of theirsystem. This substantially increases the cost of a connection but potentially reduces the installation time for thecontractor to build the entire structural frame.SECTION 4: OVERVIEW OF LABOR, MATERIAL, EQUIPMENT, INDIRECT COSTS AND MARK-UP:Material costs are based on measured quantities and quotations from vendors and suppliers. Sourcing out these costsis important specially if they are specified. Take chemical anchors for example, Hilti offers several types of anchorsand adhesives to be applied in different load applications and conditions. Cost is also dictated by the sizes of thebolts that would then dictate the amount of chemical adhesive to be used. Since steel is the main material used forstructural connections, it is important to source out actual prices. The estimator must also consider freight costs tothe project site, material handling and taxes.Labor and Equipment costs are measured in time, hours and in days. It should also be determined if a project issubjected to Prevailing Wage rates, Davis-Bacon rates or Merit Shop rates. This should be based on the location of aproject. Different cities have different rates. This determination also affects the equipment costs since this includesthe operator’s wages.6 Page

General Conditions is the contractors site overhead cost to run the project. This would cover site supervision andstaff, site office and facilities, hoisting, utilities, mobilization and demobilization costs. This also includesmiscellaneous items such as temporary fencing, traffic control, clean-up, small tools, etc.Overhead and Profit would cover the contractor’s home office overhead costs to support the project and theprofitability of the contract.Bonds and Insurance is the markup that protects and ensures the owner that the project will be completed within bidprice and time.Design contingency is used to compensate for the lack of detail in earlier stages of design. This accounts for itemsmissing as a project goes through design evolution until it reaches the final stages of design such as ConstructionDocuments (CD) level. The design contingency is often reduced to zero when drawings reach CD level, since theassumption is that at this level, everything should already have been designed and represented in the drawing set.The design contingency simply reflects the estimator’s confidence on the documents provided for estimating theproject based on things that may have been missing during design.Escalation is included in the cost estimate to account for material and labor price inflation. Escalation rates are basedon past and current market studies to forecast the pricing changes at the scheduled time of construction. It isrepresented as a percentage of the overall construction cost and usually calculated to start or midpoint ofconstruction. This somewhat protects the contractor from material cost fluctuations.SECTION 5: SPECIAL RISK CONSIDERATIONS:Steel cost fluctuation is a major risk consideration when a contractor is locking-in a bid. Steel cost fluctuates withthe price of oil, supply demand for developing countries. China has been the largest consumer for steel for the pastyears, in quantities which increased material prices throughout the rest of the world, due to the rapid economicgrowth the country has experienced. This 2015, this growth slowed down and the Chinese consumption of steel hasbeen decreased in demand and has been forecasted to continue to reduce pace through to 2016., this will result incost reduction of steel in the world market.7 Page

SECTION 6: RATIOS AND ANALYSIS – METRICS AND REVIEW FOR PROPER QA/QC:Since structural connections are usually not quantified and priced separately from the structural steel framingcomponents, metrics are not readily available for this element for estimating QA/QC, though current practices allowcarrying 15% allowance to cover the premium costs of bolts and connections.SECTION 7: MISCELLANEOUS PERTINENT INFORMATION:The estimator should also be aware if the project requires purchased materials to be manufactured in the UnitedStates under the “Buy American Act” of 2009, especially for government project. This should be part of the GeneralRequirements in the project manual (Specification). However, there are exceptions to this Act to allow thecontractor to waiver this requirement, which will not be discussed in this paper.In order to avoid conflicts with existing reinforcing in concrete structures, X-ray must be considered in the costestimate, if the connection installation involves drilling the existing concrete members to anchor or attach the newmembers . The actual locations of existing reinforcing can affect the design of the connection. This can dictate thenumber and size of anchors, the size of steel plates, thickness of welds and sizes of main members.Another aspect to consider is whether the project is a healthcare project in California. The steel component may besubjected to OSHPD requirements and inspections, which adds on a premium to the steel cost.8 Page

SECTION 8: SAMPLE DRAWINGS, SCHEDULES AND SECTIONS:RETROFIT PROJECT:Figure 1.0:On this figure, we see a partial elevation of a typical steel framing drawings. This shows the main member sizes ofthe structural frame. The connection detail is referred to detail 2 on sheet S4.2.Figure 2.0:This figure represent the connection detail referred to in Figure 1. In this figure, the connection is detailed, showingsteel dimensions, type and sizes of welds, cuts to be made to existing steel9 Page

NEW-BUILD PROJECT:Figure 3.0:On this figure, we see a typical building framing plan, showing the beam sizes and columns. The steel connectionsare represented as symbols. One dot represents typical bolted connections, double dots represent bolted and weldedconnections and a triangle to represent welded moment connections.10 P a g e

PROPRIETARY SYSTEM: (SIDEPLATE)Figure 4.0:This figure shows a typical connection detail for Sideplate connections system. These show the steel dimensions,weld type and sizes, bolt quantities and sizes.Figure 5.0:This figure shows a typical Sideplate connection schedule which supplements the detail in Figure 4.11 P a g e

SECTION 9: SAMPLE ESTIMATE:Takeoff and Pricing: For this example, Sideplate connections are going to be used.Below is a takeoff for Sideplate connection type A. This takeoff determines the weight of the plates utilized, basedon the areas and thickness of the plates, totaling to 32.9 tons.Plate ASide Plate IDLengthColumnDepth Area/PlatePlateDim. A (ft) Depth (ft.) Dim. B (ft.)(ft²)ThicknessWT ofPlate 86,793.4245,095.068C1W24X146 1.040 1,195.009WT/SFTotal for Plate A32.926 Tons12 P a g e

Below is a sample takeoff sheet on the Sideplate type counts:13 P a g e

Below is the sample steel framing estimate including the Sideplate components:QuantityUnitUnit CostTotalMetalsStructural SteelSteel columns, WF149tn 3,543.1317tn 4,148.63 71,647Floor framing288tn 4,099.28 1,179,199Roof framing160tn 4,099.28 656,582Side plate connection, type A32.9tn4,148.63 136,490Side plate connection, type B4.4tn4,148.63 18,254Side plate connection, type C1.3tn4,148.63 5,393Side plate connection, type D2.4tn4,148.63 9,957Bolts, 3/4"Ø354.0ea12.35 4,372Weld, 1/2" fillet weld2,478lf6.75 16,7271ls92,000.00 92,00032tn 4,148.63 134,104Steel columns, Tube Steel 526,155Side plate connectionsLicensing feeMiscellaneous bolts and connectionsTotal - Metals 2,850,879Subtotal Subcontractors CostGeneral ConditionsDesign Builders Bond and InsuranceGeneral Contractor FeeDesign Builders ContingencyEscalation to MOC, July 2016 2,850,879 47.01 233,683 67,860 124,521 65,539 491,603 3.85 3,834,084 55.118.2%2.2%4.0%2.0%4.0%TOTAL ESTIMATED CONSTRUCTION COSTTotal Area: 1.12 2.05 1.0860,650 SFThe total cost of the connection system (Sideplate) is 283,192, which represents 9.93% of the overall steel framingcost which translate to 4.67 per square foot. The total weight of the Sideplate connection is 6.67% of the total steelframing weight adding about 1.35lbs. per square foot of steel to the project.14 P a g e

SECTION 10: GLOSSARY:1.Moment Connections: Bolted or welded connections that can provide full moment continuity, transferringbending moments, shear forces and normal forces.2.Structural Retrofit: Adding structural components to the existing structural frame to upgrade from currentstate to the new design.3.Productivity Rate: This refers to the time a crew can perform a task.4.Takeoff: Quantification of elements on the plans for cost estimating.5.Mobilization: Refers to the contractor’s or subcontractor’s time and effort to set-up onsite, includingequipment to do a task or project.6.Demobilization: Refers to the contractor’s or subco