Concept/Preliminary design
Decisions taken at concept/Preliminary design stage will influence the extent to which the actual structure approximates to the ideal, but so will decisions taken at detailed design stage. Consideration of each of the ideal characteristics in turn will give some indication of the importance of preliminary building design. Look at the construction process in its entirety, including the contractual arrangements, the procurement route, and the level of rationalisation.
a. Safety.
The ideal structure must not collapse in use. It must be capable of carrying the loading required of it with the appropriate factor of safety. This is more significant at detailed design stage as generally any sort of preliminary design can be made safe. Pay particular attention to fire requirements however.
b. Serviceability.
The ideal structure must not suffer from local deterioration/failure, from excessive deflection or vibration. Detailed design cannot correct faults induced by bad preliminary design.
c. Economy.
The structure must make minimal demands on labour and capital; it must cost as little as possible to build and maintain. At preliminary design stage it means choosing the right types of material for the major elements of the structure, and arranging these in the right form.
d. Appearance.
The structure must be pleasing to look at. Decisions about form and materials are made at preliminary design stage; the sizes of individual members are finalised at detailed design stage.
Things that are discussed and attended to during the concept design stage:
ò Type of constructionù reinforced concrete, precast concrete, reinforced masonry, structural steel, cold-formed steel, wood, etc.
ò Column locationsùA uniform grid facilitates repetitive member sizes, reducing the cost and increasing the speed of construction. Bay dimensions may also be optimized to minimize material quantities while efficiently accommodating specific space requirements, such as parking garages and partition layouts.
ò Bracing or shear wall locationsùHorizontal forces due to wind, earthquakes, etc. must be transferred down from the superstructure to the foundations. The most efficient means of accomplishing this is usually to provide vertical bracing or shear walls oriented in each principle direction, which must be coordinated with functional and aesthetic requirements for partitions, doors, and windows.
ò Floor and roof penetrationsùSpecial framing is often required to accommodate stairs, elevators, mechanical chases, exhaust fans, and other openings.
ò Floor-to-floor heightsùAdequate space must be provided for not only the structure itself, but also raised floors, suspended ceilings, ductwork, piping, lights, and cable runs for power, communications, computer networks, etc. This may affect the type of floor system (reinforced concrete beams, joists, or flat plates; structural steel beams or open web steel joists; cold-formed steel or wood joists or trusses) that is selected.
ò Exterior claddingùThe building envelope not only defines the appearance of the facility, but also serves as the barrier between the inside and outside worlds. It must be able to resist wind and other weather effects while permitting people, light, and air to pass through openings such as doors, windows, and louvers.
ò Equipment and utility arrangementsùLarge equipment (air handling units, condensers, chillers, boilers, transformers, switchgear, etc.) and suspended utilities (ductwork, piping, light fixtures, conduits, cable trays, etc.) require adequate support, especially in areas subject to seismic activity that can induce significant horizontal forces.
ò Modifications to existing buildingsùChanging the type of roof or roofing material, adding new equipment, and removing load-bearing walls are common examples of renovation measures that require structural input.
Preliminary design
Study of Architectural Drawings
As the building is to be constructed as per the drawings prepared by the Architect, it necessary for the Designer to correctly visualize the structural arrangement as proposed by the Architect. A design engineer, after studying ArchitectÆs plans, can suggest necessary change like additions/deletions and orientations of columns and beams as required from structural point of view.
For this, the designer should have a complete set of prints of original approved architectural drawings of the buildings namely i) Plans at all the floor levels, ii) Elevations, (front, back and sides), iii) Salient cross sections where change in elevation occurs and any other sections that will aid to visualize the structure more easily .The cross sections should show the internal details like locations of windows, doors. Toilets staircases, lift machine room, staircase rooms, and any other special features like gutter at roof level, projections proposed to give special elevation treatment, etc. Always work with drawings of the same scale.
During the study following points should be noted. The drawings should be examined to find out,
ò Whether the plan shows all the required dimensions and levels so that the designer can arrive at the lengths and sizes of different members .Wherever necessary, obligatory member size as required by Architect (on architectural grounds) are given or otherwise .
ò Whether the plans and schedules of doors and windows etc. are supplied so as to enable designer to decide beam size at these locations.
ò Whether thickness of various walls and their height (in case of partition walls) is given.
ò Whether functional requirements and utility of various spaces are specified in the plans. These details will help in deciding the imposed load on these spaces.
ò Whether material/ratings for walls are specified.
ò Note the false ceiling, lighting arrangement, lift/s along with their individual carrying capacity (either passenger or goods ), Air Conditioning ducting, acoustical treatment ,R.C.C. cladding, finishing items, fixtures, service/sÆ opening proposed by the Architect .
ò Note the position/s of expansion joints, future expansion (horizontal and/ vertical) contemplated in the ArchitectÆs plan and check up with the present scope of work (indicated in the "Field Data" submitted by the field engineers).The design of the present phase will account for future expansion provision such as loads to be considered for column and footing design (combined /expansion joint footing) resulting if any .
ò Whether equipment layout has been given, particularly in the areas where heavy machinery is proposed to be located.
ò Special features like sun breakers ,fins, built- in cupboards with their sections so as to enable designer to take their proper cognizance
ò Whether the location/s of the over head water tanks specified by the Architect and whether "Field Data" submitted by field engineer furnishes the required capacity of each over head water tank
ò What type of water proofing treatment is proposed?
ò Cranes?
ò Forklift? Size, use ect
ò What is the end users intent for the structure?
ò Partitions deflections windowns
Stormwater and sewer lines along with a variety of other services such as electrical conduits lift pits and even air conditioning ducts will need to coordinate with our foundations. The optimum structural solution may need to be modified to suit these competing constraints.
Any discrepancy from above scrutiny should be brought to the notice of the Architect in an RFI, these matters should be sorted out before proceeding with any design. Try to get as many RFIÆs as possible in your first RFI, this will reduce the washing machine effect.
Choice of Structural Material
The notes that follow are an extract from Reinforced & Prestressed Concrete Design,
The Complete Process, by E. J. OBrien & A. S. Dixon.
In reading these notes keep in mind:
ò Different or extensions of existing materials, for example:
o Reinforced masonry;
o Glulam timber/reo joints for Glulam;
o Hollow precast units;
o Water-filled steel elements.
ò What priorities do the different members of the design team assign to each of the criteria given in the notes?
ò Industrial disputes also affect choice, most prominently though cost of labour.
ò Most importantly, it should be evident that new techniques/methods/systems are always emerging û keep up to date.
Introduction
The principal criteria which influence the choice of structural material are:
a. strength;
b. durability (resistance to corrosion);
c. architectural requirements;
d. versatility;
e. safety;
f. speed of erection;
g. maintenance;
h. cost;
i. craneage.
The properties of reinforced and prestressed concrete are compared below with the properties of structural steel, timber and masonry under each of these nine headings. It should be noted that only one or two structural materials tend to be used in any given construction project. This is to minimise the diversity of skills required in the workforce.
Strength
It should be noted that the ability of a material to sustain external loads is dependent on the mechanisms by which the loads are carried in a member. For example, members which are in pure compression or tension will carry their loads more efficiently than members in bending since the stress is evenly distributed across the section (this will be seen in the following section). For this reason, the available strength of a structural material depends as much on the method of load transfer as its characteristic strength. Nevertheless, it can in general be stated that reinforced and prestressed concrete and structural steel are strong materials. Relative to these, timber and masonry are generally rather weak and are more suitable for short spans and/or light loads.
Durability
The durability of a material can be defined as its ability to resist deterioration under the action of the environment for the period of its design life. Of the four raw materials used in construction, steel has by far the least resistance to such corrosion (or rusting as it is more commonly known), particularly in aggressive humid environments. Hence, the durability of a structural material which is wholly or partly made from steel will largely be governed by how well the steel is protected.
A significant advantage of reinforced and prestressed concrete over other structural materials is their superior durability. The durability of the concrete itself is related to the proportions of its constituents, the methods of curing and the level of workmanship in the mixing and placing of the wet concrete. The composition of a concrete mix can be adjusted so that its durability specifically suits the particular environment. The protection of the steel in reinforced and prestressed concrete against the external environment is also dependent on the concrete properties, especially the porosity. However, its resistance to corrosion is also proportional to the amount of surrounding concrete, known as the cover, and the widths to which cracks open under day-to-day service loads.
Structural steel, like concrete, is considered to be very durable against the agents of wear and physical weathering (such as abrasion). However, one of its greatest drawbacks is its lack of resistance to corrosion. Severe rusting of steel members will result in a loss in strength and, eventually, to collapse. The detrimental effect of rusting is found to be negligible when the relative humidity of the atmosphere is less than approximately 70 per cent and therefore protection is only required in unheated temperate environments. Where corrosion is likely to be a problem, it can often be prevented by protective paints. Although protective paints are very effective in preventing corrosion, they do add significantly to the maintenance costs (unlike concrete for which maintenance costs ire minimal).
For timber to be sufficiently durable in most environments it must be able to resist the natural elements, insect infestation, fungal attack (wet and dry rot) and extremes in temperature. Some timbers, such as cedar and oak, possess natural resistance against deterioration owing to their density and the presence of natural oils and resins. However, for the types of timber most commonly used in construction, namely softwoods, some form of preservative is required to increase their durability. When suitably treated, timber exhibits excellent properties of durability.
Masonry, like concrete, can also be adapted to suit specific environments by selecting more resistant types of blocks/bricks for harsh environments. Unreinforced masonry is particularly durable and can last well beyond the typical 50 year design life.
Architectural requirements
The appearance of a completed structure is the most significant architectural feature pertinent to material choice since the aesthetic quality of a completed structure is largely determined by the finish on the external faces. For concrete, this final appearance is dependent on the standards of placement and compaction and the quality of the formwork. Badly finished concrete faces, with little or no variation in colour or texture over large areas, can form the most unsightly views. Concrete is a versatile material, however, and when properly placed, it is possible to produce structures with a wide variety of visually appealing finishes In the case of precast concrete, an excellent finished appearance can usually be assured since manufacture is carried out in a controlled environment. Exposed structural steel in buildings is displeasing to the eye in many settings and must be covered in cladding in order to provide an acceptable finish. An exception to this is the use of brightly painted closed, hollow, circular or rectangular sections. Timber and masonry structures will generally have an excellent finished appearance, providing a high quality of workmanship is achieved. Masonry also offers a sense of scale and is available in a wide variety of colours, textures and shapes. In addition to their aesthetic fatalities, concrete and masonry structures also have the advantage of possessing good sound and thermal insulation properties.
Versatility
The versatility of a material is based as its ability (a) to be fabricated in diverse forms and shapes and (b) to undergo substantial last-minute alterations on site without detriment to the overall design. Steel can easily be worked into many efficient shapes on fabrication but is only readily available from suppliers in standard sections. Concrete is far more versatile in this respect as it can readily be formed by moulds into very complex shapes. Timber is the most limited as it is only available from suppliers in a limited number of standard sides. Laminated timber, on the other hand can be profiled and bent into complex shapes. Masonry can be quite versatile since the dimensions of walls and columns can readily be changed at any time up to construction. The disadvantage of steel, timber and precast concrete construction is their lack of versatility on site compared with in situ reinforced concrete and masonry to which substantial last-minute changes can be made. In situ prestressed concrete is not very versatile as changes can require substantial rechecking of stresses.
Safety
The raw material of concrete is very brittle and failure at its ultimate strength can often occur with little or no warning. Steel, being a very ductile material, will undergo large plastic deformations before collapse, thus giving adequate warning of failure. The safety of reinforced concrete structures can be increased by providing 'under-reinforced' concrete members (the concepts of under-reinforced and overreinforced concrete are discussed in Chapter 7). In such members, the ductile steel reinforcement effectively fails in tension before the concrete fails in compression, and there is considerable deformation of the member before complete failure. Although timber is a purely elastic material, it has a very low stiffness (approximately 1/20th that of steel) and hence, like steel, it will generally undergo considerable defection before collapse. An equally important aspect of safety is the resistance of structures to fire. Steel loses its strength rapidly as its temperature increases and so steel members must be protected from fire to prevent collapse before the occupants of the structure have time to escape. For structural steel, protection in the form of intumescent paints, spray applied cement-binded fibres or encasing systems, is expensive and can often be unsightly. Concrete and masonry possess fire-resisting properties far superior to most materials. In reinforced and prestressed concrete members, the concrete acts as a protective barrier to the reinforcement, provided there is sufficient cover. Hence, concrete members can retain their strength in a fire for sufficient time to allow the occupants to escape safely from a building. Timber, although combustible, does not ignite spontaneously below a temperature of approximately 500 ¦C. At lower temperatures, timber is only charred by direct contact with flames. The charcoal layer which builds up on the surface of timber during a fire protects the underlying wood from further deterioration and the structural properties of this 'residual' timber remain unchanged.
Speed of erection
In many projects, the speed at which the structure can be erected is often of paramount importance due to restrictions on access to the site or completion deadlines. In such circumstances, the preparation and fabrication of units offsite will significantly reduce the erection time. Thus, where precast concrete (reinforced and/or prestressed) and structural steel are used regularly, the construction tends to be very fast Complex timber units, such as laminated members and roof trusses, can also be fabricated offsite and quickly erected. The construction of in situ concrete structures requires the fixing of reinforcement the erection of shuttering, and the castings, compaction and curing of the concrete. The shutters can only be removed or 'struck' when the concrete has achieved sufficient strength to sustain its self-weight. During the period before the shutters can be struck, which can be several days, very little other construction work can take place (on that part of the structure) and hence the overall erection time of the complete structure tends to be slow. Masonry construction, though labour intensive, can be erected very rapidly and the structure can often be built on after as little as a day.
Maintenance
Less durable structural materials such as structural steel and timber require treatment to prevent deterioration. The fact that the treatment must be repeated at intervals during the life of the structure means that there is a maintenance requirement associated with these materials. In fact, for some of the very large exposed steel structures, protective paints must be applied on a continuous basis. Most concrete and masonry structures require virtually no maintenance.
An exception to this is structures in particularly harsh environments, such as coastal regions and areas where do-icing salts are used (bridges supporting roads). In such cases, regular inspections of reinforced and prestressed concrete members are now becoming a standard part of many maintenance programmes.
Cost
The cost of structural material is of primary interest when choosing a suitable material for construction. The relative cost per unit volume of the main construction materials will vary between countries. However, the overall cost of a construction project is not solely a function of the unit cost of the material. For example, although concrete is cheaper per unit volume than structural steel, reinforced concrete members generally require a greater volume than their equivalent structural steel members because of the lower strength of concrete.
Choice of Structural Form
Key Principles in Choosing Structural Form
All of the Case Studies, though on different topics, try to show that there are a number of factors that contribute, in different measures, to the structural scheme adopted. Also, it will be clear that there is no perfect answer û simply a weighted balance of the pros and cons of any given solution. Factors include:
1. Technical Requirements
ò Structure Scale:
? Stability in all directions û Vertical and Orthogonal Horizontals
? Accommodation of movement û either by joints or stress design
? Global load paths are identified
ò Element Scale:
? Proportional sizes, e.g. span/d ratios or N/20 etc.
? Global actions are allowed for in the element scheme
2. Economic Requirements
ò Materials (Refer to the handout):
? Raw cost û can it be locally sourced?
? Placement cost û e.g. block layers are expensive currently
? Transport of fabricated elements û special requirements?
ò Constructability
? Is the structure repeatable as possible
? Minimum number of trades on site
? Transport/craneage appropriate for the material considered?
3. Functional Requirements
ò Building Service Integration:
? Expect holes in beams û allow for it early on
? Flat soffits are beneficial in heavily serviced buildings
ò ClientÆs focus:
? Speculative commercial will require clear spans for example
? Landmark headquarters will possibly mean a dramatic structure
ò Architecture:
? Complement the architecture if possible
? Get involved as early as possible in the design
ò Planning:
? Minimise structural depths if required
? Drainage schemes to be appropriate to site and local drainage
? Environmental considerations
Choice of Form
The span of the structure is the main consideration. For the two usual forms of construction, the first of the following charts advises what forms of construction are appropriate for what spans for steel and concrete.
The second chart gives a comparison of the weights of structure required for various spans and types of construction for single-storey steel buildings. These buildings tend to be extremely well engineering economically.
Consider needs to be given to the coordination of mechanical, electrical, plumbing, egress, architectural, civil, landscaping, ?re-protection, security and more. You need to account for others disciplines requirements of your structure coordination areaÆs are: plumbing and process piping engineering disciplines, including but not limited to various water, waste and drainage systems, process and fuel gasses, medical gasses, vacuum services, special process fluids, as well as associated fixtures, equipment, controls and appurtenances. Service cores should be of a size sufficient size and in vertical alignment.
Examples are
ò Beam penetrations are provided for duct work and piping;
ò Slab edges are designed and detailed to accept the fascia;
ò Floor openings are coordinated with the stairs and elevators;
ò Openings are provided for mechanical shafts; and
ò Floor to ?oor height is developed considering building usage, utility and ceiling requirements.
ò Roof geometry must suite the projected usage of the facility; considering such constraints as utilities, security, piping and suspended loading.
ò Depth of roof must accommodate suspended HVAC units and other process related equipment.
ò Maximum shipping depth varies based on shop location and site location, local ordinance, over-the-road clearances, trucking availability, shop capacity or size restrictions.
ò Maximum shipping length varies based on trucking availability, local ordinance, shop crane capacity, shop size restrictions, site laydown area, installation crane capacity, and handling and lateral stability requirements.
ò Maximum weight of shipping piece varies based on trucking availability, local ordinance, shop crane capacity and installation crane capacity.
ò Bracing geometry should suite the usage of the facility, considering openings, and other penetrations and circulation requirements in the ?nal facility.
ò Elevations must be coordinated with the ?nal usage of the facility or ?nished elevation requirements.
ò Shoring requirements, special erection needs, design assumptions very helpful additions to the design documents.
ò The lateral stability of the structure is a function of the initial design assumptions, the erection sequence and the erector- installed temporary bracing. Regardless of the nature of the structure, the erector is responsible for the lateral stability as it is installed. The erectorÆs temporary bracing must therefore sustain the forces imposed on the structure during the installation process. For the erector to accomplish this, the documentation should identify the lateral-load-resisting system and connecting diaphragm elements that provide for lateral strength and stability in the completed structure; and any special erection conditions or other considerations that are required by the design concept, such as the use of shores, jacks or loads that must be adjusted as erection progresses to set or maintain camber, position within speci?ed tolerances or prestress
Concrete
Design of concrete framed facilities also requires a similar under- standing of the construction process and coordination. Variables such as those listed below are examples of such considerations:
ò Shoring and re-shoring requirements.
ò Loading and support of concrete.
ò Form de?ection limits.
ò Concrete ?nish requirements.
ò Joint location and details in slabs on grade and walls.
ò Precast shipping restrictions or trucking availability.
ò Cold or hot weather concreting procedures noted within the design documents.
ò Layout of column anchor bolts including the foundation rein-forcing provides the basis for accurate initial construction.
Simple considerations such as the selection of wall thicknesses must be done in concert with structural engineering needs as well as accommodating mechanical and electrical elements within the walls. Allowances for the depth of framing, piping, ductwork, suspended ceilings and similar concealed items must be considered as part of the overall design, especially if any of the systems must be stacked within a space. Mechanical systems including heating, ventilation and air conditioning, gas and water pipes and vents, and fire protection systems where applicable generally present the greatest impact on structural systems. The size of ductwork and piping elements and accommodation for the changes in direction of these systems requires provision for openings, chases and horizontal bulkheads that impact placement of structural framing.
Electrical systems which include electric power, lighting, communications (voice, media and data) and controls generally fit within the structural framing without major problems due the small size and flexibility of wiring and conduits. However, these systems have become increasingly more complex in terms of the amount of wiring. This complexity is of particular concern with advanced systems like Structural Insulated Panels or other closed panel products. In addition, lighting appurtenances such as fixtures, control panels, built-in components and similar features occasionally create problems which must be resolved by altering the framing design, moving framing elements or moving the electrical wiring or devices.
The coverings that make up the typical structural system also interact in direct and indirect ways with the ability to keep moisture from becoming a problem in the building. The selection of certain materials that either attach to the structural system or are part of it can create a situation in some climates where the material acts as an unintended vapor retarder and thus retains moisture from either inside or outside the building. Bulk water movement into the building also can be influenced by the structural system. For example, it often is necessary to cut through the structural sheathing to run plumbing and mechanical vents. To reduce the potential for leaks, the design of the venting systems should be coordinated with the structural system design. Even the slope of the roofÆs structural members can impact water penetration and should be considered.
In addition to the space limitations relative to mechanical systems discussed previously, there must also be adequate provision in terms of wall, floor, or roof thickness to accommodate insulation.
FoundationÆs impact on utilities and moisture
The foundation system can interact in at least two significant areas with other systems in the building moisture management and utilities. The elevation of the foundation can be too low for proper placement of utilities, or it can be placed to preclude effective drainage. The first case can lead to bulk water entry into the basement or crawlspace. It can also result in failure of the sanitary sewer if the slope is too low for adequate gravity discharge. In addition, just the very presence of utility openings creates potential routes for water entry. In the second case, the flow of water toward the building is one of the most common reasons for wet basements.
Utilities can also be damaged or destroyed if the foundation is not designed to accommodate them. Piping that runs through a foundation is a good example where the allowance for a sleeve should be part of the structural system design. Otherwise, it is not uncommon for plumbing supply and sewer pipes to be sheared at the point of entry through the foundation. Failures can also occur if copper piping is buried in aggressive soils or directly in contact with concrete. The structural system should consider these types of systems interactions in the design stage.
Finally, the foundation system can interact with the thermal envelope to create moisture problems under the right conditions, especially with crawl space construction. Placement of insulation in the floor of a crawlspace typically requires foundation ventilation. Under the right circumstances, this approach can contribute to the very moisture problems it is intended to prevent. Thus, an economical structural solution may create a negative outcome because of failure to reconcile it with the thermal envelope design.
General design steps
1. Always start with preliminary sketches, creating your own plans of the structure elements from the architects drawings will remove congestion of ideas from the paper and give you an idea of the building concept. As with any structure, conceptually determine the type of system that best meets the layout, size, budget, fire-protection, loading and expected durability. Butter paper is good for this task.
2. Draw/sketch frames indicating the number of stories (including the vertical expansion proposed for design).and number of columns forming the particular frame
3. With a framing concept in hand, do some preliminary sizing calculations to set structure depths and verify that the concept will adequately support the loads and meet serviceability criteria.
4. Identify slab or beam runs and frames. Name all the frames of the layout, number span and columns members
ò All beams of the same types having approximately equal span (+) or (-) 5% variation), magnitude of loading, support conditions and geometric property are grouped together . the heaviest beam of the group is considered for the design. In the preliminary beam design, value of reaction at both ends are worked out for all the loadings acting on the beam.
ò Beams shall be treated as
o A rectangular beam if it does not support any slab on either side.
o As L-beam if it supports a slab on one side an
o As T-beam if it supports slab on both sides.
5. Write the relevant column and beam numbers involved in the frame.
6. Dimension the storey heights (including plinth to footing level) and spans of beams.
7. Show the type of joint at foundation assumed for analysis (i.e. fixed or hinged at bottom).
8. Show all the loads coming on the beams and nodal vertical and horizontal forces.
9. The preferred solution. pattern loading is not required for dead load, (which eliminates some of discrepancy in flat slab design between the tables of coefficients, and accurate analysis). It is therefore necessary, for flat slabs to consider a few loading cases, which are calculated for working loads and then factored for ultimate load. These are: Dead load on all spans, live load on even spans, and live load on odd spans. To these should be added the analysis for the prestress loading, wind and any other loadings. For both ultimate and serviceability design.
10. Design the reinforcing for these beam runs
11. For columns that are not part of the lateral force resisting system, do the design and detail them.
12. Identify which beams might participate in lateral resistance (for moment frames) and create models to analyze the overall building for wind and seismic
13. Design the reinforcing for the lateral system beams and columns.
14. Design any shear walls that are used.
15. For beams acting as collectors, re-design with added tension or compression forces and supplement the reinforcement accordingly.
16. For unique situations, floor openings, special concentrated loads, floor drops, ramps and stairs, provide design efforts on these special areas and adjust supporting beams and columns as necessary Depending on the form and intended use of the building other effects may need to be considered, for example:
- Braking and Impact forces in buildings where vehicles are present.
- Effects of earth pressures & ground water on basement walls
- Buoyancy effects
-
17. Vertical or Lateral effects of machinery
18. Design the footings.
19. Get all your documents Signed off on sections and details prior to them going to the CAD department. (A cursory review and signoff of sections and details by the senior engineer is required to catch mistakes before sending sections and details to the CAD department. Such a review saves time and is informative for the engineer whose details are being critiqued.)
Loadings
Before starting the final design it is necessary to obtain approval of the preliminary drawings from the other members of the design team. The drawings may require further amendment, and it may be necessary to repeat this process until approval is given by all parties. When all the comments have been received it is then important to marshal all the information received into a logical format ready for use in the final design. This may be carried out in the following sequence:
-checking of all information
-preparation of a list of design data
-amendment of drawings as a basis for final calculations.
Checking of all information
To ensure that the initial design assumptions are still valid, the comments and any other information received from the client and the members of the design team, and the results of the ground investigation, should be checked.
Stability
Ensure that no amendments have been made to the sizes and to the disposition of the core and shear walls. Check that any openings in these can be accommodated in the final design.
Movement joints
Ensure that no amendments have been made to the disposition of the movement joints.
Loading
Check that the loading assumptions are still correct. This applies to dead and imposed loading such as floor finishes, ceilings, services, partitions and external wall thicknesses, materials and finishes thereto.
Make a final check on the design wind loading and consider whether or not loadings such as earthquake, accidental, constructional or other temporary loadings should be taken into account. In general the load case including permanent, imposed, and wind load will be most onerous for all elements, however it is not normally considered necessary to include wind load for members that do not form part of the direct wind resistance system as the wind load effects will be small and can be neglected. However local effects do need to be checked.
Fire resistance, durability and sound insulation
Establish with other members of the design team the fire resistance required for each part of the structure, the durability classifications that apply to each part and the mass of floors and walls (including finishes) required for sound insulation.
Foundations
Examine the information from the ground investigation and decide on the type of foundation to be used in the final design. Consider especially any existing or future structure adjacent to the perimeter of the structure that may influence not only the location of the foundations but also any possible effect on the superstructure and on adjacent buildings.
Performance criteria
Establish which codes of practice and other design criteria are to be used in the final design.
Materials
Decide on the concrete mixes and grade of reinforcement to be used in the final design for each or all parts of the structure, taking into account the fire-resistance and durability requirements, the availability of the constituents of concrete mixes and any other specific requirements such as water resisting construction for basements.
Hazards
Identify any hazard resulting from development of the scheme design. Explore options to mitigate.
Questions for Identifying Presence of Errors
These are provided to help you review your work, generally the engineer in charge will not have the time to check all you calculations, Thus YOU need to check these a thoroughly as you can.
i. Is the deflected shape consistent with what was expected? When reviewing displaced shape from analysis software, look for beams that rotate at beam-column connections; evaluate whether you intended for the connections to be rigid or not. Verify that the beams you expected to deflect most actually do. Verify that the frames you expected to deflect most under lateral Do.
ii. If most beams are the same size, why are the others not? Evaluate whether you would expect the different beam to be bigger, smaller or the same.
iii. Are the moment diagrams consistent with what was expected? When reviewing moment diagrams from analysis software, look for columns not part of the lateral load resisting system that have moment at the base; evaluate whether the support should be or not. Look for torsion in girders; evaluate whether you intended for the beam-girder connections to cause torsion or not. Verify that the locations where you expected negative have negative moment. Verify that the locations of points, points of zero moment, are where you expected them.
iv. Is the beam depth consistent with standard rules-of-thumb?
v. For lateral load in any direction, do the connections and bracing provide a continuous load path to the foundation? This is why it is good to Draw cross-sections through the entire structure,
vi. Does the building weigh what you anticipate?
vii. Does total base shear equal total applied lateral load?
viii. Do connection details match the assumptions used in the analysis? Identify locations in the structure where you intended to have a rigid or semi-rigid connection
ix. Are the primary structural member sizes similar to members in similar projects?
x. Do beams deflect more than permitted?
xi. Intuitively and instinctively, would you want to walk under it, live above it, and climb on it?
xii. Pipe penetrations, HVAC supports, electrical manholes, civil elevations and locations and the like. Has the conduit been considered? If you overlay the plans, do things line up. Are there dimensional errors between discipline drawings? The most common error I've found is the locations of building using coordinates. If you check the coordinates on the corners of a building, does the dimensions match the structural drawing?
xiii. Before passing on any work to the next stage ask yourself, are you happy with it?
xiv. A variety of tactics are employed when performing reviews. Those tactics areas follows:
a) Look at the big picture.
b) Verify load paths.
c) Review framing sizes.
d) Look at connection details for constructability.
e) Look for mistakes.
f) Look for subtleties.
g) Look at the drawings for constructability.
h) Review for clarity.
i) Look for omissions.
j) Look for ôlittleö little things.
k) Look for the ôbigö little things.
l) Verify that the structural drawings match the architectural and MEP drawings.
m) Look for mistakes
n) ò Look for the subtleties
o) ò Look at the drawings through contractorÆs eyes.
p) ò Look at the drawings through contractorÆs eyes.
q) ò Review for clarity/consistency
r) ò Look for omissions
s) ò Look for ôlittleö little things
t) ò Look for ôlittleö little things
u) ò Look for ôbigö little things
v) ò Structural dwgs. match Arch. dwgs.?
w) ò Structural dwgs. match Arch. dwgs.
òAny unrealistic load paths?
òLoads jumping in/out of shear walls / braced frames?
òAny unrealistic ôrigidö diaphragms?
òAny loads on the structure not in the computer model?
Typical framing to verify model
ò Typical framing to verify model
ò Major load carrying members
ò Wind and seismic loads
ò Unique framing not in computer model
Items requiring special attention:
Elevators
Escalators
Folding partitions
Special hang points
Facades
Davits
Special hang points
Rooftop MEP loads
Heavy hung piping
Stairs
Monumental stairs
Hangers
Special loads on joists
Horizontal loads from rigging
Hangers
Theater rigging
Catwalks
Expansion joints
Check connections:
ò Critical connections
ò Unusual connections
ò Connections w/ complex geometry
ò Connections w/ large reactions
. Look for mistakes:
ò Wrong reactions
ò Members too small
ò Improper framing configurations
ò Not enough reinforcing steel
ò Punching shear problems
ò Missing structural integrity reinforcing steel
ò Missing sections and details
ò Mistakes in sections and details
ò Column splices at inappropriate locations (mid-height of 80Æ unbraced height).
ò Columns mistakenly assumed to be braced by mezzanines.
ò Floors diaphragms w/ insufficient strength/stiffness to brace columns
Look at drawings through the eyes of a contractor:
ò Everything shown that will allow contractor to build structure without having to guess or issue RFIÆs?
ò Every linear foot of building perimeter covered by a section?
ò Everything clearly indicated?
ò Can drawings be interpreted by someone whoÆs not an engineer?
. Review for clarity & consistency:
ò Look for conflicts between framing plans and sections/details.
ò Inconsistencies with framing
ò Inconsistencies with framing
Group similar beams
Consistency = simplicity = economy
ò Drafting inconsistencies
Look for omissions:
QA reviews
ò Missing things often hardest to find
ò Missing:
Section and details
Dimensions and elevations
Sizes
Reinforcing steel
