Quantity Surveying 16
AHouse Construction Report
AHouse Construction Report
Soundproject management is a major contributor to the success of anyconstruction project. Poor workmanship and insufficient attention todetails by the constructors are some of the causative agents of thedefects that are experienced in some buildings after theirconstruction. As such, this report aims at exploring the varioussteps of a building construction, from the foundation level toroofing. The various structural elements such as beams walls, floorjoist and trusses will be evaluated by considering safe and economicconstruction methods, as well as material specifications. The reportpresents several diagrams showing the details of the various parts ofthe building. However, more significantly, it should be understoodthat the core of this building report is based on ground conditionand the type of soil, fill foundation, cavity brick wall and timbertrusses. The report then concludes that safety is a key considerationin any construction project.
Itis important to follow proper procedures when constructing structuressuch as buildings. The construction procedures are wholly dependenton the geological properties of the site where the structure is to beset up. Also, thorough site investigation should be carried out toavoid any failures in the future. Subject to research, siteinvestigation is the procedure through which geotechnical, geologicaland other important ground condition data, which may influence theexecution of a construction, are studied. During site investigation,the questions of the building durability and the general safety ofits occupants are asked. This report aims at delving deeper into thevarious structural elements of a building with an intention ofevaluating the safety measures and economic construction methods, aswell as material specifications.
Thisreport is for a typical single-story house construction at churchfield Garston. It comprises 100 mm thick concrete and masonry wallsthat support the roofing structure. A 30 degree gable is appropriatefor the roofing, which entails galvanized steel sheets that aresupported by timber trusses. The roof should be flexible to cater forseismic disturbance.
SiteInvestigation and Groundwork
Significanceof Site Investigation in Choosing Foundation Type
Formost projects, a more intricate method is required, and it willgenerally follow the course below.
Emmittand Gorse (2006, p.2), siteinvestigation is a process of gathering geological, geotechnical andother essential ground data that may affect the construction of abuilding the information is and taken to the laboratory for ascientific analysis. Through the data gathered, the durability andthe general safety of the occupants of the proposed building can beevaluated. Soil and rocks have varied characteristics that may eitheraffirm or nullify a proposed design of a building (An & Di 2016,p.245). It is because soils and rocks play an important role indetermining the foundation safety of a structure. As a result, withthe data regarding the soil and rock characteristics, preliminarydrawings are made, which also include the types of foundation.Therefore, the choice to construct a building build on a given siteis usually premised on its entire appropriateness from theperspectives of engineering.
Someof the site data that is needed include rock formation and theirgeological structure, soil profile, bearing capacity, shear strengthand plasticity index. Such data is crucial in any construction ofheavy structures from low-rise buildings to skyscrapers and waterformations, such as weirs and dams. The information regarding thenamed parameters is essential in selecting the foundation type forany particular structure. It is because the bearing capacity of asoil varies from one type to the other. Since the discovery of soilengineering, the black cotton soil has been known to have low bearingcapacity than sand. Therefore, this poses a serious danger to thefoundation and ground floor slabs because of swellings that resultfrom ground pressure uplift (Dematteis & Soldo 2015, p.255).Consequently, having information regarding the type of soil found ona particular site will inform the type of foundation to be chosen,such as raft groundwork. On the other hand, pad foundation footing ismostly applicable for sand soils due to low differential settlement.
Itis vital to ascertain the facets of the proposed construction in asmuch as they have been chosen. Besides, care should be considered toset up the possible loading circumstances, as well as the sensitivityof any structures to be constructed, or those already available nearthe site, to the modifications that will happen as a result ofbuilding. For instance, the movements due to excavation may destroytunnels and services passing below or near a proposed digging for abasement (Menkiti,Long, Milligan, & Higgins, 2014, p.1429).Moreover, the structures above a proposed tunnel may be destroyed bymodifications in the groundwater circumstances.
Thenecessity for certain foundation types for cut slope, retainingwalls, and special construction processes, for example, dewatering, agrouting, and ground enhancement should be established this is drawnfrom the combinations of construction and ground conditions.Therefore, such will bring with them certain limit states. There willbe a necessity to fulfill geotechnical analyses, in cases where limitstates cannot be evaded (for instance, by altering the pattern of theproposed structure). Above all, the course of all site explorationshould be one of scientific approach. There should be enough factualdata gathered (walk-over survey and the desk study) to come up withhypotheses concerning the ground conditions (Menkiti,Long, Milligan, & Higgins, 2014, p.1428).Thus, from such analysis and a rational understanding of what is tobe set up on the site, the challenges that are likely to arise duringthe construction and the life of the project must be established. Thedesign of the proposed structure should consider the project’sgeotechnical background this is in a bid shun as many challenges anddecrease the remainder. Lastly, ground examination should beconducted properly to establish the real circumstances on the site,as well as to get parameters for engineering computations. Whetherfield investigation is by boring/ drilling or geophysics, it shouldhave noticeably established aims if it is to be valuable. In certaininstances, it may be crucial to do broad and thorough groundexamination. Presently, ground study is defectively targeted, and itis for this reason that it is at times regarded as a compulsory butrather unfulfilling expense. Nevertheless, it is notable that themajority of unanticipated charges associated with construction aregeotechnical in nature(Hse.gov.uk.2016).
Thefoundation for this building has cast in-place buttressed concretepiers. When the soil is firm, wall footings are used they are 0.3mdeep and 0.6m wide, 10mm mild steel transverse rebar with 250mmcenter-to-center spacing, and 12mm high tensile steel longitudinalrebars. However, when the soil is soft, cast-in-place piers areapplied. The tie-beams are normally 0.4m deep, 0.3m wide with 3, 12mmhigh tensile steel longitudinal rebars at the top and below, as wellas 10mm mild steel sloping rebar (200mm center-to-center spacing)(Menkiti,Long, Milligan, & Higgins, 2014, p.1428). Typically,the piles are spaced 3.0m apart alongside wall lines they have a300mm diameter and are 4.0m deep with 4 No. Notably, 10mm mild steeland 16mm high tensile steel longitudinal rebar transverse rebar at200mm center-to-center spacing. Typically, the concrete has a 28-daycompressive strength of 21 MPa (3000 psi) this applies for bothtypes of foundations. The areas between the tie beams containslab-on-grade concrete structure as depicted earlier for the instanceof shallow foundations.
Belowis a sample diagram of a house foundation:
TheEffects of Clay and Rubble on the Foundation
Expansivesoils pose huge risks to foundations for the low-rise lightbuildings. Swelling that results from the ribbles always causesuplift pressures of almost 5,600 PSF (Kelly, Graham, & Male2014). This can cause serious damages to light structures such aswooden wood-outline buildings. These expansive soils, majorly clay,contain hygroscopic earth minerals such as sodium ions that swell andincrease in size when in contact with water molecules. This causesuplift pressures as outlined above, and, therefore, leads to variousstructural consequences.
Themost evident path in which clay soils can damage foundations is byuplift forces as they swell due to moisture absorption. Consequently,the swelling soils lift up and break the strip footings. In mostcases, it causes serious distress in the ground floor slabs. Giventhe distinctive structural loads on various parts of a foundation,the resultant uplift will fluctuate in various regions as describedin Fig. 1. below (Hussein, Kiang, & Kim 2015, p.365).Accordingly, the structural corners have a tendency to be lifted upon the focal segment. This is normally exacerbated by moisturedifferentials in clay soils at the edge of the structure. This iscalled differential settlement and, consequently, the foundationsuffers distress that may interfere with structural stability andsafety.
Figure1 Uplift Pressure in Clay Soils[ CITATION AnD16 l 1033 ]
Excavationand Plant Safety
Excavationsmust follow the set safety procedures, especially, if on cohesivesoils and in frail rock. This is because such soils can only standunsupported for periods running from 30 seconds to 30 days (An &Di 2016, p.250). In any case, care should be taken since it isdifficult to predict the exact time the sides will collapse. It isexpected that both sides of the excavated area be supported firmly.Support is expected to forestall collapse and to guarantee the safetyof the building occupants and the neighbours. After the supports havebeen erected on both sides of the excavated area, the zone ofinfluence needs to be estimated as shown in Fig. 2 below (Kelly,Graham, & Male 2014). The mechanical plants such as vehicles,excavators or some other overwhelming loads ought not to be situatedin the `zone of influence` of excavation. The ground support that isrecommended and introduced should be placed by skilled personnel,such as a geotechnical specialist, to prevent the dynamic forces thatmay cause the side-walls of an excavated area to collapse.
Thedetermination of the zone of influence will rely on the groundconditions. It is the zone in which there may be an influence on theexcavation, including conceivable ground collapse. Any material willadd a load to the region where it is put. Therefore, it is criticalthat materials are not put or stacked close to the edge of anyexcavated areas. Moreover, to lessen the danger of ground collapse,excavated or free material ought to be put away from the excavation.The excavated material ought to be set outside the determined zone ofinfluence (Hussein, Kiang, & Kim 2015, p.364). On the other hand,a ground support ought to be planned and introduced to convey theextra loads, including any ground water pressures and saturated soilmaterials.
Figure2 Ground Support and Zone of Influence[ CITATION Hos15 l 1033 ]
Ithas been observed that the strip or fill foundation, as shown above,is favourable in sites with expansive soils such as clay. The mainreason for such observation is based on the fact that there islimited if no distress to the ground floor slabs due to the presenceof suspended rafts. Also, the disturbances caused by differentialsettlement of clay soil are very minimal, thus leading to durabilityand safety of structures (Kelly, Graham, & Male 2014).
Siteinvestigations must be carried out to uncover the likely soilconditions of the proposed site after which, a stepwise methodologyis employed to execute various structural elements.
Thefollowing procedure should be followed in this case:
Treesand hedges in site location should be cleared to create room forexcavation and consequently, construction of various structuralelements.
Trenchfill foundations in expansive clay soils have a wider zone ofinfluence. As such, there is a need for heave precautions.Compressible soil materials ought to accurately put in place tocontain the swelling clay soils in the excavated area.
The foundation`s sides must be as vertical as possible and should never be battered at any point.
The ground floors where the clay soil settlement is expected should be suspended with a ventilation void space under it. This will eliminate any heave circumstances that may ensue due uplift pressures.
Duringsetting, the sides of the excavated trench should be kept verticalwhile the floor is levelled. The following should be taken intoaccount:
Ensure that the design thicknesses of diver leaves and the recommended exaction dept as per the engineering drawings.
The substructure must be built halfway on the excavated trench foundation.
Ensure that the diagonals and structural estimation are precise.
Excavationand Blinding Layer
The cavity wall to be central on blinding layer.
Minimum strength and thickness of blinding layer should be 15kN/m2 and 100mm respectively.
Foundation trenches must be widened at the pier locations to ensure the recommended projection dimension.
Foundation width should not be less than that recommended in the Building Regulations manual.
Unless structurally specified, where concrete is to be cast directly into the earth, the reinforcement to be used must have not less than 70mm nominal cover.
The trench bottom must be horizontal as possible.
Waterand Debris in Trenches
Any debris and water present in the foundation trenches must be removed before concrete casting is commenced.
ConstructionJoint and Reinforcement
Thesteel reinforcement bars for the foundation strip should be as perthe design specified sizes.
If plastic shuttering is to be used for the ground beams, all care ought to be taken so that shuttering or the earth backfill material supports formwork properly before concrete is cast.
The formwork must be straight for the correct depth of cover to the steel reinforcement bars to be achieved.
Unnecessary concrete joints should be avoided as much as possible
Steel or corrugated formwork or even clean and smooth timber boarding should be used.
The trench foundation dimensions must be able to accommodate the cavity walls as centrally as possible.
The concrete blinding layer for the foundation must be levelled.
The diagonals must correspond to the design specifications before erecting the substructure cavity walls.
Masonry cavity walls should be set out to achieve the recommended cavity widths.
Brickwork must be set to the edges of the trench foundation or corbelled to ensure that there are no rectify cavity widths.
GroundBearing Floor Construction
Topsoil and any organic matter must be scrapped off and removed and the underlying layer levelled.
Ground floor slabs to be constructed should be specified and the fill earth material must be compacted in several layers not exceeding 225mm with no pieces that go through a 75mm ring diameter.
In cases where the depth totals of earth fill material under the ground floor slab is more than 600mm, a suspended raft foundation floor construction to be provided.
Fill material used must be free from any harmful and toxic substances.
Fill material should be prepared as certified by a recognized competent laboratory procedure regarding their engineering fitness for purpose. They must also be chemically checked and analyzed before use.
Theyare reinforced concrete and shear walls devised under the guidelinesof BS 8110.The 100 mm concrete block 28-day compressive strength isnormally 3.0 MPa (one unit) (Gov.uk.2016). Theconcrete block units are 200 mm high by 100mm thick by 400 mm long.All mortar mixes are typically of 1-part cement to 3 parts sand. Limeis usually not used. When the concrete blocks are used, wallintersections, rebar is placed vertically in the cells and groutedwith a wet mix. However, this is ineffective because the dimensionsof the cell are too small relative to the rebar for adequatecompaction (that is, 10mm and 25mm respectively), and the grout w /cis too high.
ExternalWalls Damp Proof Membrane
Check that the hardcore infill is compacted to the recommended degree and covered with blinding made of sand to ensure that even support is provided for the DPM (insulation).
DPM membranes must not be less than 1200 gauge. The thickness can be increased and should be a Radon or any other gas barrier is to be required. Additional provisions for the laps or service pipe insertions also apply.
DPM sheets should be overlapped by not less than 150mm.
In cases that DPM is sited underneath the concrete floor slab, it must also be underneath any insulation material level, especially, when that insulation material is less resistant to ground impurities.
The DPM to be turned up at floor slab edge and lapped below the DPC for the complete thickness of the interior leaf to make a continuous barrier.
MaterialMember Specifications (Dematteis& Soldo 2015)
Conventionalmasonry walls must be constructed with an interior and exteriorleaves while a cavity is provided separating the two. It must beconstructed as per the following guidelines:
The cavity must have not less than 50mm width
It must be kept free of mortar snots so that it is never bridged
The exterior and interior leaves must be tied appropriately as per the design specifications.
The cavity may be completely or partially insulated, depending on wind and rain exposures. For incomplete fill insulation, not less than 50mm of the cavity must always be provided.
Wallties must meet the following conditions:
They must be as specified in BS EN 845-1.
They must be suitable for the recommended width of cavity and be not less than 50mm leaf bearing
They must be laid to a minor fall towards the external leaf and to have the capability to bind insulation against the inner leaf for incomplete fill scenarios.
Lateralrestraint straps must be provided where necessary and must be as perthe design specifications.
Brickand block suitability
Facing masonry bricks must be durable, especially regarding frost and moisture resistance.
All external masonry block work must be rendered or to be finished with a durable cladding.
Masonry blocks always vary in color. The color chosen must be as per the client needs.
Mortar category over DPC course must be by design manual to ensure adequate durability, workability, and strength.
Batching and mixing machines and equipment must be kept clean to avoid contaminations.
The mortar should be mixed by the mixing machine or the already mixed ones to be used.
Mortar must be carefully and constantly proportioned, and then methodically mixed using an automatic mixer, except for very miniature quantities.
Thisshould be carried out by a licensed quantity surveyor
Thefoundation dimensions should be fully considered and thoroughlychecked (Dematteis & Soldo 2015).
Formworkor Plastic Shuttering
TheFormwork or plastic shuttering should be carried out as outlined inthe specification books. The figure below gives more details aboutthe specifications.
Settingout of the walls
Thetrench foundations must be of the correct width to accommodate thecavity walls centrally.
Drainageand Service Entries
Thedraining pipes passing through the external walls must be secludedthrough lintels and or ‘rocker pipes’.
TheDPC membranes should be provided as shown below in the figure below.
HorizontalDamp Proof Courses
Wherea DCP membrane is to be sited over the floor construction but put inplace laid before the superstructure is fully completed, it isrecommended to install a 450mm wide of DPC, which must be lapped ontothe interior leaf before cavity wall (Panda et al. 2014, p.298).
Windows& External Door Frames
Windows& External Door Framesmust be carried as per the designspecifications.
Roof& Guttering must be constructed as per the design specifications
Slabsare to be designed under limit state method by reference of BS 8110
When the slabs are supported in two way direction it acts as two way supported slab.
A two way slab is economical compared to one way slab
Fck= 15 N/mm2 FY =415 N/m2
Shorterspan: – Lx = 5.8m longer span: – Ly =7.62m
CheckLx/Ly= 7.62/5.8 =1.3<2 Hence the slab has to be designed as “twoway slab”.
Providingover all depth of slab as 5”, 120mm eff. depth= D-15-Ø/2=120-15-10/2=100mm
Condition:- supported on four sides.
Deadload = 25×0.12×1 = 3.0KN/m
Liveload =2×1 = 2.0KN/m
Floorfinish =1×1 = 1x1KN/m
Totalloading = 6.0 KN/m
Bendingmoment calculation:- (code)
Typeof panel: – Two adjacent edges are discontinuous
Ax(+)= 0.049 ax(-) = 0.065 ay(+) = 0.035 ay(-) = 0.047 (+ve)
B.Mat mid span in shorter directions.
Mx(+)= ax(+)wlx2 = 0.049x6x5.8^2= 9.9kn-m factored
B.M= 9.9×1.5 =14.85kn-m
Spacingand diameter: As per sp-16. Provide 8mmØ bars at 210mm spacing.
(-ve)B.M at continuous edge in shorter direction. Mx(-) =ax (-) wlx2=0.062x6x (5.8) ^2 =13.12kn-m factored B.M = 13.12×1.5=19.67kn-m
(+ve)B.M at mid span in longer directions. My (+)= ay(+)wlx2 = 0.035x6x(5.8) ^2 =7.06kn-m factored B.M=7.06×1.5 =10.69kn-m
(-ve)B.M at continuous edge in longer direction.
My(-ve)= ay (-ve)wlx2 =0.047x6x (5.8) ^2 =9.48kn-m factored B.M=9.48×1.5=14.22kn-m. 27
Checkingfor depth: Permissible depth=100mm Mu.lim =0.36.Xumax(1-0.42Xumax) fckbd^2 d 14.86×10^6= 0.36.Xumax(1-0.42×0.48)15x1000d^2
d=84.71 < 100mm
Hence,they are acceptable(Riley & Cotgrave 2008,p.12).
There should be no less than 50 mm void space between the ground floor beams and fill earth material.
The beams should be placed onto a DPC membrane at the bearings.
The beams should be suspended by brick piers of not less than 200 mm by 200 mm cross section surface.
It should be ensured that the cavity material fill is not less than 225 mm below the lowest level of the DPC.
The ventilation voids at the two opposite cavity walls must be provided to the ground floor one with a required provision of not less than 1500 mm2/m run.
A DPC should be provided above the finished ground floor slab just under the party wall.
SafeConstruction method for the Upper Floor
Engineeringevaluation and detailed design
Allthe timber frames should be designed within the specified parametersof BS 5268 or Eurocode 5 (BS EN 1995-1).
Itis significant that the slab is put up within the tolerancesspecified for the timber frame since the cavity wall panels areplaced on sole metal plates, which rest on the slab.
Thescaffolding is necessary to ensure the safety of the occupant. Allthe scaffoldings must meet the recommended threshold.
Theteam charged with site erection must be completely trained andbriefed properly to ensure that the floor joists and timber frame areconstructed in a safe manner and accordance with the designrequirements/
Theroofing arrangement is deemed a `deck` system because a truss is notusually used. It is a system of sheeting, secondary and main beams.The sheeting is normally corrugated or patterned galvanized steelsheet of 26 g thickness. It is supported on treated timber beams(100mm wide by 50mm deep), or 100mm cold-formed steel Z-sectionpurlins (Panda et al. 2014, p.299). In the former case, the timberbeams span 1.2m, and the Z-purlins span 3.0m. The main beams orrafters are typically 200 mm deep if of timber, but of 100mm deepmild steel I-section if of steel beams. The floor is a 100mm thickconcrete slab-on-grade reinforced with steel fabric, 142 mm2/m. Theconcrete typically has a 28-day compressive strength of about 21 MPa(3000 psi).
MaterialSpecifications for Warm Deck Flat Roof
The finished roof should have a slope of not less than 1 in 80.
Theroof should be drained in one edge or two edges.
­The traditional gutters are enhanced than interior outlets. ­
The waterproofing should extend up adjacent to the cavity walls of not less than 150 mm (6 in) in all situations from the roof surface.
The top most edge of the waterproofing material should be protected by a nominal cover flashing.
The insulation must be as per the Part L of the Building Regulations.
The bitumen membranes should be covered from the sun as per the surface protection manual.
All the roof materials such as insulation and membrane sections must be constructed to guard against wind forces.
TheTimber Truss Construction
Unloadingis the riskiest of all activities involved in timber trussconstruction. The unloading process must be done as cautiously aspossible.
Thetrusses must be stored safely either horizontally or vertically atground level. This helps in safe and easy removal.
Asa rule, the use of mechanical handling is advised. This reduces therisks to the workers. Also, the lifting levers and hydraulics must beas stable as possible to avoid an accidental fall, which may havefatal consequences.
Assemblyof Trussed Rafter Roofs
Oncethe timber trussed rafters have been raised safely to eaves level,the assembly is recommended to commence following buildingconstruction specifications.
Thetimber trusses must by braced to ensure stability and reduce the riskof collapse.
Insummation, the main aim of this report was to explore the variousstages of building construction from the foundation level to theroofing. The various structural elements such as beams walls, floorjoist and trusses have been evaluated by considering safe andeconomic construction methods, as well as material specifications.Specifically, the report has focused on the soil type and groundconditions. After reviewing the various aspects of a buildingconstruction, it can be concluded that safety is paramount.Therefore, it should be a major consideration in all the stages ofbuilding construction, from site investigation to the finishingoperations.
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