8/10/2019 SE1 Design Practice Guidelines http://slidepdf.com/reader/full/se1-design-practice-guidelines 1/59 HongKongHousingAuthority HongKongHousingAuthority HongKongHousingAuthority HongKongHousingAuthority S SS S SS S SS T TT T TT T TT R RR R R R RR U UU U U U UU C CC C C C CC T TT T T T TT U UU U U U UU R RR R R R RR L LL L L L LL DD DD D D D DD E EE E EE E EE S SS S SS S SS I II I II I II G GG G GG G GG N NN N NN N NN PP PP P P P PP R RR R R R RR A AA A A A AA C CC C C C CC T TT T T T TT I II I I I II C CC C C C CC E EE E E E EE
DESIGN AND DETAILING OF SUPERSTRUCTURE22 Zoning of Concrete Grade 1623 Zoning of Wall reinforcement 1624 Minimize Transverse Links for Columns/Walls 1725 Reduce Torsional Links at Transfer Girder 1826 Laps in Column Contributing in Lateral Load Resisting System 2027 Good Detailing Practices
27.1 Lapping of Heavy Bottom Bar at Column Face 2027.2 Waterstop at Expansion Joint 2127.3 Minimum Spacing of Column Vertical Bars 21
27.4 Spacing Intervals of Wall Reinforcements and Beam Stirrups 2227.5 Minimum Support Width 2227.6 Use of Epoxy Coated Bars 22
28 Slenderness of Walls and Columns 2229 Movement at Base Restrained Walls 2330 Beam-Column Joint Design 25
REFERENCES 26
APPENDICES Appendix A Templates for Design Synopsis 27
- Design Synopsis for Foundation 28
- Design Synopsis for Superstructure 35 Appendix B Guidelines for Structural Design Review 46 Appendix C Efficiency Indicator 51 Appendix D Commonly Used Design Loading Intensities 55A di E T l t f D t i i F di L l f LDBP 57
This document provides reference guides to the general structural designpractice adopted in SE Section 1, but it is important to recognize that the
validity of applications may be different for different projects. The usersshall exercise own judgment and make adjustment as appropriate to suittheir projects’ specific needs on a case by case basis.
Where discrepancy in the content arises between this document and theQuality Manuals, the provisions of Quality Manuals shall prevail.
2. CONTROL OF DOCUMENT
The document is issued and reviewed under the authority of CSE/1.Feedback on this document is welcome and should be addressed to theContact Point who is now SSE/2. This document will be annually reviewed.
3. DESIGN S YNOPSIS
To ease independent check and cross reference between individual projects,presentation format of design synopsis has been aligned in SE Section 1 asdepicted in Appendix A.
4. STRUCTURAL OPTIMIZATION PSE shall carry out structural optimization to achieve an economical designbalanced for buildability considerations. Some basic principles include:
5.1 Independent Design CheckTo enhance the design reliability of projects with increasinglycomplex site-specific designs and frequent updating of more andmore powerful software, PSE shall conduct independent checks on
structural design in a rational and effective manner. Beforefoundation tender out, the computer models and loading scheduleshould be checked by an independent checking engineer assignedby the PSSE within the same design group. For the superstructure,a more comprehensive checking shall be conducted according to the
“Guidelines for Independent Check of Structural Design” which can
be downloaded from the Knowledge Management Portal or SE1Sectional Share Drive. Refer to Appendix B for detailed timing ofconducting the independent checks.
5.2 Semi-automated Data Management System (SDMS)The SDMS, comprising a series of data processors, has beendeveloped in-house to automate design activities across the rangeof common software in use. It is a multi-functional tool facilitatingthe design processes from foundation to superstructure, includingloading plan preparation, SAFE modeling, pile schedule generationto detailed design of walls, lintel and transfer beams etc.
PSE should make use of the SDMS to enhance process efficiency anddesign reliability. With the use of SDMS, the entire design processis automated with less risk of computing error, leading to savings intime and resources for counter-checking, and expeditingoptimization cycles thus enabling reliable confident functional and
Design contingency may be allowed to cater for minor design changes orscope increases required as the design evolves. It is not intended to cover
extensive design changes or significant scope increases. The designcontingency may be different for different projects depending on thecomplexity and maturity of the projects at the time of consideration, butnormally it should not exceed:
Dead Load : +0% (Dead + Live) Load :
- horizontal elements (not wind resisting element): +0%- other elements above Transfer: +5~10%- other elements at Transfer and below: +15%
7. DESIGN LOADING I NTENSITIES
With the increasing use of modular flat design (MFD), a list of commonlyused design loading intensities is complied at Appendix D for reference.
8. MODELING OF TRANSFER BEAM/P LATE
As a conventional design method, it is generally acceptable to carryout structural design of the transfer beam/plate without considerationof the stiffening effects by the walls. However, it is prudent to checkthe interaction effect (e g horizontal stress) in designing the wall
Provision in the Hong Kong Building (Construction) Regulations (B(C)R)should be followed in live load reduction. Except those at PlantRooms/Meter Rooms, all live loads at typical floor should be reducible.
Design contingency may be allowed to cater for minor design changes orscope increases required as the design evolves. It may be different for
different projects depending on the complexity and maturity of the projectsat the time of consideration, but normally should not exceed:
For transfer and below : +5~10% Above transfer : +5%
11. MODELING APPROACH
Exclude non-essential elements in the wind model as far as possible tominimize number of elements subject to detailing for ductility.
Torsional stiffness of beams may be neglected in the case ofcompatibility torsion as per ACI 318 Code (i.e. torsion is induced solelyby the angular rotation of adjoining members such that redistributionof torsional moments to adjacent members can occur via alternativeload paths). However, torsional stiffness should be considered forcases involving equilibrium torsion (i.e. torsional resistance is requiredto maintain static equilibrium).
12. R ESERVED W ALL OPENING
According to technical guideline DCG-D-1302 (MF-201) of MFD issuedunder DCMBI No D06/09 PSE should work with project team to evaluate
13. MODELING OF UPPER R OOF (U/R) AND GROUND FLOOR (G/F)
Minimize number of U/R wall elements in wind model to alleviate theimplication of possible future change in U/R layout.
Minimize number of ground beams to allow trenches, openings,box-out etc. which may be required by other parties.
Exclude G/F beams of relative small bending stiffness in wind resisting
system to alleviate the difficulty of lapping column bars at middlequarter of the storey height.
14. R EVIEW THE USE OF COLUMNS AND W IND - RESISTING BEAMS
Review the need of columns and wind-resisting beams to address the morestringent detailing rules. For example:
To design element as wall instead of columnFor columns of relatively high aspect ratio (e.g. D/B>3), adjust theratio to slightly greater than 4, if practicable, to turn the column into awall to escape the ductility requirements in detailing for columns.
To align the depth of floor beams with corridor slab Aligning the depth of floor beams with that of the corridor slab canescape the minimum support width requirement.
As the ductility requirement at Section 9.9 of Concrete Code assumesthe formation of plastic hinge at critical sections of beams, theestimated value of EI should be that for the stage just before the onsetof yielding. To allow for the corresponding effects of cracking, the
assumption of half bending stiffness for beams should be justified.Either full or half bending stiffness thus may be accepted on projectbasis provided that a consistent approach is adopted for all lintelbeams throughout analysis.
To simulate structural walls coupled by lintel beams in finite elementmethod, the use of wall shell elements with coarse mesh would tendto be relatively stiff in bending and attract more stresses to the lintels.Wall shell elements with finer mesh would attract less stresses to thelintels.
Save for stability requirement, torsional stiffness of lintel beams can beignored (Also refer to Paragraph 11).
16. ELASTIC MODULUS OF CONCRETE
The elastic modulus corresponding to the mean concrete strength (insteadof characteristic strength) may be used in checking the overall response ofbuilding to wind loads, including checking against the H/500 criteria for
deflection at the top of a building. The mean concrete strength may bereferred to Table 3.1 of BS EN 1992-1-1:2004, which is derived from thecharacteristic compressive strength ƒcu by the following relationship:
respectively. Hence, they all exceed the characteristic strength by more
than 10MPa. The above formula thus gives relatively conservativeestimates of mean cube strength and should be reasonably safe for use indesign. Typical values of elastic modulus corresponding to the meanconcrete strength as derived from the above formula are:
Characteristic cube
strength, ƒcu (N/mm 2)
Mean cube strength,
ƒcm (N/mm 2)
Mean value of elastic
modulus, E cm (kN/mm 2) 35 45 26.440 50 27.745 55 28.9
Nonetheless, the exact method of deriving the mean value may be agreedwith ICU in advance through pre-submission enquiry.
17. CORRIDOR SLAB/B EAM MODELING
Allow services zone of preferably minimum 250mm width along corridor for
18.2 Bell-out diameterWhen the permanent liner is terminated above the inferredrockhead level (Fig. 1) or at least 0.3m above the bell-out (Fig. 2),greater pile bearing capacity can be achieved by adopting a bigger
bell-out based on the shaft diameter at rock socket ( ∅-0.2) insteadof the net shaft diameter at permanent liner ( ∅-0.3).
In determining founding level of LDBP, the following criteria are tobe met:-
- Total Core Recovery is based on 1.5m core run.- Founding level should have at least 5m thick of competent rock
below the pile base in accordance with the pre-drill information.- Pile base is at least 0.8m deep into bedrock for LDBP with bell-out,
but maximum 30 degree bell-out angle will control the socketlength when bell-out diameter exceeds shaft diameter by morethan 0.92m. Besides, to avoid collapse of the bell-out underunstable weathering rock, bell-out should normally be completelyembedded into the bedrock. As such, the minimum socket length
may be governed by the socket length of bell-out tool at openposition.
- Minimum rock socket depth of 0.5m for categories 1(a) and 1(b),and 0.3m for categories 1(c) and 1(d) along the pile perimeter isrequired.
- To avoid possible settlement problem, there should have no weak
seams within the depth of 0.5 times bell-out diameter below thefounding level, even if the total core recovery (TCR) requiredwithin the 1.5m core run is satisfied.
PSE shall complete the template for determining founding level ofLDBP at Appendix E for discussion in the Design Review (F) meeting.
In order to minimize the pile re-design works due to small change inactual founding level, the effective design length of LDBP in pileanalysis can be taken as the pile length measured from the cut-offlevel down to the inferred rockhead level plus half of pile shaftdiameter instead of the founding level.
18.5 Pile Capacity Based on Combined Frictional and End BearingResistanceThe use of combined capacity may be considered in the followingsituations to increase the load-carrying capacity for piles socketed inrock: -
- When a particular short pile exists in a large pile group, it tendsto attract more axial load due to the relative high stiffness. Tocompensate for the increase in attracted forces, the pile capacitycan be enhanced by shaft friction with socket into rock.
- When Cat. 1(b) rockhead can be reached within short distancebelow inferred Cat. 1(c) rockhead, it may be advantageous toeliminate the bell-out by utilizing the combined capacity of shaftfriction at Cat. 1(c) rock and end-bearing at Cat. 1(b) rock tosave cost and/or time in construction.
Using higher concrete grade at lower floors generally can save cost. Theoptimum floor for change of concrete grade to achieve the maximum
saving can be determined by comparing alternative models with costanalysis. As a quick reference, the optimum floor may be assumed atabout 1/3 of the building height for a 40-storey building based on previousexperience.
On the other hand, it is also justified to use grade 35 concrete throughoutshorter building structures of less than 27 storeys (i e 2/3 of 40 storeys)
Structural Cost of Walls Vs Floor
$100,000
$150,000
$200,000
$250,000
$300,000
$350,000
$400,000
$450,000
$500,000
$550,000
$600,000
$650,000
$700,000
$750,000
$800,000
$850,000
R F
F 4 0
F 3 9
F 3 8
F 3 7
F 3 6
F 3 5
F 3 4
F 3 3
F 3 2
F 3 1
F 3 0
F 2 9
F 2 8
F 2 7
F 2 6
F 2 5
F 2 4
F 2 3
F 2 2
F 2 1
F 2 0
F 1 9
F 1 8
F 1 7
F 1 6
F 1 5
F 1 4
F 1 3
F 1 2
F 1 1
F 1 0
F 9
F 8
F 7
F 6
F 5
F 4
F 3
F 2
Floor
C o s t
Option 1 (Total)
Option 2 (Total)
Structural Cost of Walls Vs Floor
$100,000
$150,000
$200,000
$250,000
$300,000
$350,000
$400,000
$450,000
$500,000
$550,000
$600,000
$650,000
$700,000
$750,000
$800,000
$850,000
R F
F 4 0
F 3 9
F 3 8
F 3 7
F 3 6
F 3 5
F 3 4
F 3 3
F 3 2
F 3 1
F 3 0
F 2 9
F 2 8
F 2 7
F 2 6
F 2 5
F 2 4
F 2 3
F 2 2
F 2 1
F 2 0
F 1 9
F 1 8
F 1 7
F 1 6
F 1 5
F 1 4
F 1 3
F 1 2
F 1 1
F 1 0
F 9
F 8
F 7
F 6
F 5
F 4
F 3
F 2
Floor
C o s t
Option 1 (Total)
Option 2 (Total)
C35
C45 Optimum floor for change ofconcrete grade to achieve themaximum saving
Fig. 1 Structural Cost of Walls of Different Concrete Grades
The bar spacing at the floor of new zoning should preferably be the sameas that of preceding floor by modifying the bar diameter only, if possible, toease construction or avoid confusion.
24. MINIMIZE TRANSVERSE LINKS FOR COLUMNS /W ALLS
For columns, only each alternate bar should be supported by a link.Limiting the maximum vertical bar spacing of columns to 150mm from arestrained bar can substantially reduce transverse link as illustrated below:
This, however, is not applicable to the ‘critical regions’ of columns inaccordance with Cl. 9.9.2.2(b) of the Concrete Code, where eachlongitudinal bar or bundle of bars shall be laterally supported by a linkpassing around the bar and having an included angle of not more than135 .
Similarly, limiting the maximum vertical bar spacing of walls to 200mm
from a restrained bar can reduce transverse link (when Asc > 2%).
25. TORSIONAL LINKS AT TRANSFER GIRDER
The diameter of torsional links should be preferably not greater than T16.Transfer girders subjected to larger torsional effect are mainly those aroundthe re-entrant bay. Some suggested ways to minimize torsional effect toease the site fixing problem are:
(a) To model the wall above the transfer girder in gravity modelModeling the wall above the transfer girder and restraining its tophorizontal translation in the minor axis direction can reduce thetorsional effect considerably in some case studies. Ensure that theinduced stresses on the wall element as a result of the interaction effect,especially the shear stress, are designed for.
(b) To add tie beam Adding tie beams to restrain the rotation degree of freedom of thetransfer girder can reduce the torsional effect considerably dependingon the beam sizes and positions. Prior agreement with the projectteam to allow sufficient space below the beam soffit for the passage ofdrainage pipes is required.
(c) To align transfer girder with the wall above Aligning the centre line of the girder with the wall above is the mosteffective way in lessening the torsional effect. However, it should benoted that the clear column spacing at the re-entrant area at groundfloor will be reduced, and additional bends of drainage downpipes arerequired to avoid possible physical conflict with the protruded portion ofthe transfer girder into the re-entrant.
Passage fordrainage pipes
Re-entrant
Additional tie-beam
Protrusion into re-entrantobstructing the passage ofdownpipe
26. L APS IN COLUMN CONTRIBUTING IN LATERAL LOAD RESISTING SYSTEM PSE should try to avoid laps of column bars at middle quarter of the storeyheight. Except for columns terminated at pile cap as well as above andbelow transfer plate, Clause 9.9.2.1(d) of the Concrete Code can be waivedif it can be shown that a column plastic hinge adjacent to the beam facecannot occur by satisfying the following condition:
ΣMc ≥ 1.2ΣMbwhere
ΣMc is the sum of the moment capacities under the appropriate axialload of the column sections above and below the joint; and
ΣMb is the sum of either the clockwise or anti-clockwise moment
capacities of the beams on both sides of the joint, whichever is thegreater.
For G/F columns terminated at pile cap/footing, the storey height may bemeasured from the top of pile cap (instead of G/F level) to the 1/F providedthat the G/F beams are of relative small bending stiffness in wind resisting
system. Column bars can be lapped at G/F level same as the normalpractice with just slightly longer lap length. This helps alleviate thedifficulty of lapping column bars at middle quarter of the storey height.
27. GOOD DETAILING P RACTICE
27.1 Lapping of heavy bottom bar at column faceWhen heavy bottom bars are required at beam-column joint, lap thebottom bar at the column face as illustrated below. Beams shouldbe as wide as or wider than the column into which they frame, ifpracticable In addition to formwork economy this alleviates
27.2 Waterstop at expansion jointIn installing waterstop along expansion joint (EJ), rebar interferenceproblems are occasionally spotted especially at thin structuralmembers with heavy reinforcement. Some good typical details tohouse the waterstop at EJ are suggested below:
27.5 Minimum Support WidthThe minimum support width specified in the Code will limit themaximum size of re-bar. Use splay or stud beam at support iflarger diameter of re-bar is required.
27.6 Use of Epoxy Coated BarsEpoxy-coated bars are mandatory to be used in all water-retainingstructures except in external works. The maximum bar diameteravailable in the market as reported in some projects is ET20. PSEshould check the availability of bar size in local market when agreater bar size is proposed.
28. SLENDERNESS OF W ALLS AND COLUMNS
Slenderness of walls and columns especially those from foundation level totransfer level should be checked. Design the walls and columns as stockymembers or provide additional reinforcement.
In checking wall slenderness, wall return in flanged or core walls can beused to stabilize the edge of the adjacent planar wall. If the outstandlength of a wall is less than 6t, it may be considered to be fully restrainedagainst out-of-plane movement independent of the distance between floor
Cracking is often observed in base restrained concrete walls. It occurs fora number of reasons, which may or may not be predictable, including:
(a) Movement induced or restrained by neighboring construction
consisting of rigidly connected parts but concreted at different times A typical example is in the case of walls cast against previouslyconstructed pile caps. Because of the construction sequence, thewall and its base are out-of-phase in terms of shrinkage and early agethermal movement, giving rise to differences in deformations and thuscracking due to restraining action of the rigid connection.
Fig. 4 Typical crack pattern for base restrained walls
The subsequent floors poured will shrink at a greater rate than thepile caps concreted at earlier times. The out-of-phase shrinkage willbe further aggravated if large concrete pour (e.g. massive transferstructures) is involved on subsequent floors. The contraction andhence inward movement of which can exert a horizontal movementthus inducing shear cracking at base restrained walls.
Fig. 6 Cracks at a G/F wall as a result of movement restraint
(b) Differential vertical movement along the wall baseDifferential vertical movement along the wall base can occur underload leading to shear cracks due to two main aspects. The first is therelative vertical deflection of the horizontal elements supporting thewall (e.g. cap and transfer structure etc). The second is thedifferential movement of the foundations (e.g. footing, pile).
It should be prudent to observe the above movement at base restrained
30. BEAM-C OLUMN J OINT DESIGN Design of beam-column joint stipulated in Cl 6.8.1.2 of Concrete Code,
as confirmed by ICU in SLG Meeting No. 14, should be based onyielding load of the rebars (i.e. actual area of steel provided) per theHKIE Handbook approach except that the overstrength factor can betaken as 1.0 instead of 1.25 (i.e. T=C=1.0Asfy);
Cl. 6.8 of Concrete Code applies to all beam-column joints in bothlateral loading resisting frames and non-lateral load resisting framesalike;
For beam-column joint without upper column, it would have axial forcevarying from zero at top to the axial reaction from lower column atbottom of the joint arising from the beam loads. Hence, average ofaxial force across the joint (i.e. half of the axial force of lower column)may be taken for calculation of horizontal and vertical jointreinforcement in accordance with Equation 6.72 and 6.73 of Concrete
Structural Design Practice Appendix A - Design Synopsis for Foundation
GUIDELINES
Introduction
1.1 Description of the ProjectInclude a general description of the site and the development
1.2 [Status and]* Scope of submissionDescribe scope of submission [including submission history and identifyingmajor design changes for amendment submission]** for amendment submission only
Describe relevant referrals to and comments from other departments andorganizations, if appropriate.
1.3 Site Characteristics and Geological InformationInclude:a. A general description of the characteristic features of the site and
surrounding environment, including slopes, existing foundations andretaining walls etc.
b. Summary of geological information, including results of necessary field andlaboratory test reports etc.
Design Approach
1.4 Foundation System and Design AssumptionsInclude:a. A general description of the foundation systemb. Methods and assumptions used on the design of foundation system
Appraisal on the Effects of Foundation Works on Adjacent Lands and
Structures1.5 Effects of foundation works on adjacent slopes and retaining wall
/adjoining buildings /existing utilities within the site etcDescribe the assessment of the foundation works on adjacent lands andstructures at both construction and permanent stages.
Structural Design Practice Appendix A - Design Synopsis for Foundation
EXAMPLE
1.1 Description of the Project
The proposed site of the [Project Name] is located at ……………….. The proposed developmentcomprises one domestic block of 35 storeys and other associated external works.
1.2 [Status and]* Scope of submission
For first submission
This submission covers the design of the piling foundation system for the domestic block. Pilecap is not covered in this submission and will be submitted separately.
For amendment submission*
1.2.1 The foundation submission for the design of piling system was approved by ICU on XX.XX.2010.
1.2.2 This amendment submission covers mainly the following: -(a) ……………………………..; and(b) Other minor amendment.
1.3 Site Characteristics and Geological Information
According to “Geotechnical Report (FDN) No. S34/08” at Appendix C, the Site was formed by
reclamation in late 1970s with average ground level at about +5.5mPD. The Site is generallyunderlain in succession by fill with average 4m thickness, marine deposits with thickness ranged
from 1m to 6m, in-situ decomposited Granite with thickness ranged from 0m to 8m and then
bedrock level may vary between -3mPD to -39mPD dipping from northwest to southeast in
generally.
Architectural Services Department (ArchSD) has demolished the existing buildings except the
existing piles, pile caps and footings below ground levels, special care and provisions will be
allowed for overcoming possible obstructions of the abandoned piles, pile caps and footings for
Structural Design Practice Appendix A - Design Synopsis for Foundation
1.4 Foundation System and Design Assumption
The foundation system adopts large diameter bored pile (LDBP) of 2.2m and 2.5m effective
shaft diameter with bell-out diameter 3.45m and 3.9m respectively bearing on and/or socketted
into Category 1(c) rock (i.e. Grade III or better rock with total core recovery of not less than 85%
and min. uniaxial compressive strength of rock material (UCS) not less than 25 MPa (equivalent
point load index strength PLI 50 not less than 1MPa)). The pilecap is 2.5m thick and is designed
to be one continuous single mass covering the whole footprint of the building and supported by
15 nos. LBBPs.
All vertical loads are taken by end bearing and/or socket of LDBPs founding on Cat 1(c) rock
with allowable bearing capacity of 5000kPa for end bearing and 700kPa for bond of the socket.
All horizontal loads are resisted by the bored piles and cap through subgrade reaction.
Allowable horizontal movement at the pile cap bottom level is to be 25mm.
The foundation design is based on the following assumptions:
Negative skin friction on pile is not applicable.
Design water table is assumed to be at about +3.5 mPD i.e. 2m below existing ground level.
Self-weight of the bored pile embedded is not included in the calculation of bearing capacity
of pile.
Design length of the bored pile to be counted from cut-off level to inferred rockhead plushalf of the effective shaft diameter or actual rock socket length, whichever is shorter.
Piles are assumed to be fixed to the pile caps at the top and pinned at the toe.
A reduction factor of 0.8 was applied to concrete stress of piles to account for concreting
under water.
Allowable bearing capacity of pile to be increased by 25% solely due to wind forces.
In-plane moment acting on walls is converted to equivalent up and down axial point loads
for SAFE input.
All forces in the loading schedule are calculated down to the pile cap top level only, To cater
for the difference in levels between the top of pile cap and the pile cut-off, additional
Structural Design Practice Appendix A - Design Synopsis for Foundation
in the pile cap, Wood Armer Method is selected for the analysis in SAFE v8.0.6. Piles are
modeled as spring supports with the use of rigid arms to simulate the pile rigid zone.
1.5 Appraisal on the Effects of Foundation Works on Adjacent Lands and Structures
No slope, retaining walls and adjoining buildings are within or around the subject site.
A 6-m wide drainage reserve (DR) transverses the Site at the north- west and is about 30m
away from the nearest LDBP. To ensure the stability of DR, settlement markers & piezometers will be installed as shown in the “Drainage Reserve Area and Monitoring Plan"
1.6 Design Code and Reference
Code of Practice for Foundations
Code of Practice for the Structural Use of Concrete 2004
Hong Kong Building (Construction) Regulations
1.7 Design Data
1.7.1 Concrete and Reinforcement Properties
a. Concrete for all LDBPs to be Grade 45/20D with a minimum crushing strength offcu = 45 N/mm2 at 28 days.
b. As LDBPs are cast under water, design concrete strength=0.8 x 45 N/mm2 = 36N/mm2
Young’s Modulus of Concrete E = 23970 N/mm2 (Short Term)E = 11985 N/mm2 (Long Term)
c. Concrete for pile cap to be Grade 40/20D with a minimum crushing strength of fcu= 40 N/mm2 at 28 days
Young’s Modulus of Concrete E = 25100 N/mm2 (Short Term)E = 12550 N/mm2 (Long Term)
d. Concrete density = 24 kN/m3 and Poisson ratio = 0.2
e. Concrete cover to all reinforcement of LDBPs to be 75mm
Structural Design Practice Appendix A - Design Synopsis for Foundation
1.7.3 Characteristic Load Cases
Dead load (DL), live load (LL),wind load (WL) from blocks
Obtained from loading schedule of drawing Nos. XXX/BLK1/S/EF003
4 wind load cases are considered. Soil load (SL) on top of cap Soil thickness = 1.5m
Soil unit weight= 19kN/m3 Self-weight of cap Cap thickness =2.5m
Concrete unit weight= 24kN/m3 Stud wall Obtained from loading schedule
Lift impact load Impact load= 290 kN/ lift for Pilecap Design only
Mass concrete fill to pits of LiftNo. 1 & 2
Mass Concrete thickness = 1m Concrete unit weight= 24kN/m3
Transformer room loading at G/F LL= 65 kN/m2
1.7.4 Design Load Cases and Load Combinations1.7.4.1 Load Combination for Pile Bearing/Socket Capacity and Stability Checking
1.0(DL+LL) < Ground bearing-capacity of compression pile without Wind
1.0(DL+LL+/-WL) < Ground bearing-capacity of compression pile withWind
1.0(DL+/-WL+U*+ I a#
)<
R a Ground bearing-capacity of tension pile 1.0DL+/-1.5WL+1.5U*+2.0Ia# < 0.9Ru (Stability Checking against Uplift,
Overturning and Buoyancy)
*Where U is the buoyancy to the pile cap due to highest possible waterlevel assumed at ground level.#Where I a is the adverse imposed load including live and soil loads.Where R a is the allowable uplift resistance of pile shaft + effective self
weight of pileWhere R u is the ultimate anchoring resistance of the pile
1.7.4.2 ULS Load Combination for R.C. Design of Pile
Structural Design Practice Appendix A - Design Synopsis for Superstructure
GUIDELINESIntroduction
1.1 Description of the ProjectInclude a general description of the site and the development
1.2 [Status and]* Scope of submission
Describe scope of submission [including submission history and identifyingmajor design changes for amendment submission]** for amendment submission only
Describe relevant referrals to and comments from other departments andorganizations, if appropriate.
1.3 Description of the Building Structures
Include:a. A general description of the building structure and foundation systemb. Structural form and material (e.g. irregular in plan configuration, precast
elements etc)c. Highlights of unusual areas
- Structural form (e.g. truncated storeys, split level)- Elements (e.g. transfer plate, large cantilever)
Structural Design Practice Appendix A - Design Synopsis for Superstructure
1.4.4 Lateral stability shall be provided by shear walls and cores acting in conjunction with
the floor slabs and tie beams which act as a rigid diaphragm to distribute the wind loadhorizontally. The wind force is progressively distributed to the shear walls and cores oneach floor via the floor diaphragm and subsequently transmitted to the foundations.
1.4.5 Where walls are linked by lintel beams or floor slabs, these walls are treated ascoupled shear walls and the developed coupling effects in the structural members aredesigned for accordingly. The applied-moments due to the wind forces are resisted bya combination of moments in the walls and the couple arising from the axial forces inthe walls. The bending action of walls induced shears in the lintel beams, which exert
bending moments, of the opposite sense to the applied wind moments.
1.4.6 The robustness of the blocks is in compliance with the Code of Practice for StructuralUse of Concrete 2004 (HKCC) in consideration of the following:
The layout of the buildings are checked to avoid any inherent weakness; The building is designed to resist a higher horizontal load due to wind load than
the notional horizontal load; the buildings are provided with effective horizontal ties
i. around the periphery by precast façade & slab ;ii. internally by slab & beam ;iii. to column and wall by slab & beam.
Structural Design Practice Appendix A - Design Synopsis for Superstructure
1.6 Design Standards and Sources of Reference
The following Codes of Practice and Standards are adopted for the design of this project:(a) Hong Kong Building (Construction) Regulations 1990(b) Code of Practice on Wind Effects in Hong Kong 2004(c) Code of Practice for Structural Use of Concrete 2004(d) Code of Practice for Precast Concrete Construction 2003(e) PNAP APP-68 for cantilever structures(f) BS8007 - Water Retaining Structures 1987
1.7
Design Data1.7.1 Reinforced Concrete - Materials
1.7.1.1 Concrete
The concrete grades adopted in the design are as follows:
Element Level Concrete
Grade
CharacteristicStrength fcu(N/mm²)
Pilecap 40/20 D 40G/F, F2–F40,above Roof 35/20 D 35Slab & Floor BeamF1 and Roof 45/20 D 45F1 to F20 45/20 D 45Corridor slab (300mm thk)F21 to F40 35/20 D 35
Transfer Beam F1 45/20 D PFA 45Transfer Plate F22 45/20 D 45
F1 to F20,Roof 45/20 D 45Lintel Beam & Tie BeamF21 to F40 35/20 D 35FoundationLevel to F20 45/20 D 45Wall and Columnabove F20 35/20 D 35
Precast Façade All 45/20 D 45Parapet and In-situStaircase All 35/20 D 35
Precast Staircase All 35/20 D 35Water RetainingStructures Water 45D/20(W) 45
Structural Design Practice Appendix A - Design Synopsis for Superstructure
1.7.1.2 Reinforcement
All reinforcement shall be in compliance with Type II deformed bars toConstruction Standard 2 (CS2) and have the following properties:
Type II deformed bars to CS2 f y = 460 N/mm2 Mild steel bars f y = 250 N/mm2
Modulus of elasticity of reinforcement E s = 200 kN/mm2
The minimum size of bars shall be 10mm unless otherwise specified. All reinforcement for water tanks shall be epoxy coated bars.
1.7.2 Cover to Reinforcement
Cover to reinforcement refers to:(i.) Code of Practice for Fire Resisting Construction – 1996 (HKFC)(ii.) Code of Practice for Structural Use of Concrete – 2004 (HKCC)(iii.) HD Structural Engineering Technical Guide – (DSEG-104)
FRP of the various compartments in the building is stipulated in the approved generalbuilding plan and its requirement on concrete cover and element size are tabulated forcomparison with the HKCC. The more stringent requirement governs the design. Thecover refers to the distance of all reinforcement to the surface unless otherwise stated.
Storey Usage FRP(hr.) Element
Cover (c), min.& size (s), min.
for FRPto HKFC
Cover,nominal forDurability toHKCC or forDurabilityand FRP toDSEG-104
Structural Design Practice Appendix A Design Synopsis for Superstructure
1.7.3 Design Loading
1.7.3.1 Gravity Load
Dead and imposed loads shall be in accordance with the Hong Kong Building(Construction) Regulations (B(C)R) 1990. Reduction of the imposed loadscomplies with Part III of B(C)R 1990.
Floor slabs shall be designed for loads imposed by partitions at the particularlocations indicated on Architectural drawings. Where partition details are notgiven on the Architectural drawings, allowance for partition loadings shall bemade in accordance with Part III of B(C)R 1990.
(a) Dead LoadReinforced concrete = 24.00 KN/m³Concrete partition (excluding plaster) = 24.00 KN/m³Plaster/tile to all walls = 22.60 KN/m³Panel wall partition = 20.00 kN/m³
(b) Imposed Loads and Finishes:-
Level Elements FinishesKN/m²
Imposed LoadKN/m²
Upper Roof General Roof Top Area (Accessible)General Roof Top Area (Non-accessible)Lift Machine RoomLift Shaft Top Slab
2.02.01.01.0
2.00.7510*26*
Main Roof Refuge Area/Raised deck passagewayEmergency Generator RoomBooster Pump Room
Structural Design Practice Appendix A Design Synopsis for Superstructure
(c) Construction Load Finishes Imposed loadG/F – designated area 0 20
1.7.3.2 Wind Load
Design wind loads shall be in accordance with the Code of Practice on WindEffect in Hong Kong 2004 (HKWC).
The building height (upto Main Roof) = 114.95mThe least building horizontal dimension = 54.9m (Wind direction = 105 o )
Aspect ratio of the least dimension = 2.09 < 5
As the building height is greater than 100m, the resonant dynamic responseof the building shall be considered in the design in accordance with Section 7of HKWC.
6 nos. of reversible wind directions of 0 o, 33o, 90 o, 105 o, 123o and 165 o areconsidered to be critical for the building. A loading contingency (5%) is appliedto facilitate the future submission.
The maximum lateral deflection due to wind forces has been checked not toexceed 1/500 of the building height.
1.7.4 Design Load Cases and Combinations
ULS Load Combination
Load Type
Dead ImposedLoad Combination
Adverse Beneficial Adverse Beneficial Wind
1. Dead and imposed 1.4 1.0 1.6 0.0 --
2. Dead and wind 1.4 1.0 -- -- 1.4
3. Dead, imposed and wind 1.2 1.0 1.2 0.0 1.2
Structural Design Practice Appendix A - Design Synopsis for Superstructure
AP- PSSE/PSE to brief CSE/1 on the preliminary structural scheme before AP- PSSE/PSE to propose a design review programme for CSE/1’s agreement- Interim Review Note 1 normally involves CSE/1, PSSE and PSE. Other attendees
may be proposed by CSE/1 or PSSE as appropriate
EAP/P1- Conduct at least 1 Interim Review before EAP/P1- PSE to build up preliminary computer models once DD(DC) has agreed in principle
on the selected building form without anticipated significant further changes (Exacttiming depends on the project programme, complexity and political considerationsetc)
- Provide preliminary efficiency indexes for reference
P2- Conduct 1 more Interim Review before P2- Preferably provide estimated cost data on the superstructure at about 1 month
before BC- Conduct Design Review (S)Note 2 between P2 and BC
- Design Review (S) to be chaired by CSE/1 and attended by all SSEs, graduatesand design SEs nominated by SSE
Piling TO
Structural Design Practice Appendix B - Structural Design Review
2. Professional Services Provider (PSP) Design Projects
AP- PSP/PSSE/PSE to brief CSE/1 on the preliminary structural scheme before AP- PSP to propose a design review programme for CSE/1’s agreement- Interim Review Note 1 normally involves CSE/1, PSP, PSSE and PSE. Other
attendees may be proposed by CSE/1 or PSSE as appropriate
EAP/P1- Conduct at least 1 Interim Review before EAP/P1- PSP to build up preliminary computer models once DD(DC) has agreed in principle
on the selected building form without anticipated significant further changes (Exacttiming depends on the project programme, complexity and political considerationsetc)
- Provide preliminary efficiency indexes for reference
P2- Conduct 1 more Interim Review before P2- Preferably provide estimated cost data for the superstructure at about 1 month
before BC
Piling TO- PSP to conduct Design Review (S)+(F)Note 2 at piling TO.
- Design Review (S)+(F) to be chaired by CSE/1 and attended by all SSEs anddesign SEs nominated by SSE
To enhance cost-effectiveness in structural design, a series of EIs have beendeveloped, comparing the structural efficiency of various design alternativesagainst the criteria for function and quality. These EIs greatly facilitate designteam to arrive at fully optimized and highly cost-effective structural designs.
Typical tables of comparison of EI for foundation and building are attachedbelow for reference.
Structural Design Practice Appendix C - Efficiency Indicator
[5] Piling Benchmark is applied to piling design of 40 domestic storey blocks.
+
Y The reinf & concrete figures are estimated.
PILING BENCHMARK [5]
For 223 H-Pile, Total Net Pile Capacity (kN) = [Total Pile No. x 3016 (kN) - Total NSF (kN)] where 3016kN is allowable bearing capacity of pile with group reduction factor 0.85.
For Footing, Total Net Pile Capacity (kN) is not applicable.
A
[2] Total D+L is the total load at top of pil e cap from loading schedule excluding self-weight of pile cap and the fill above the cap.
[3] Total Net Pile Capacity should deduct any NSF.
B
Unit Rate of Material
For LDBP, Total Net Pile Capacity (kN) = [Total Shaft Area (m2) x 9000 (kN/m 2 ) - Total NSF (kN)] where 9000kN/m 2 is allowable direct compression of 45D/20 concrete concreting under water. As a general guideline, LDBP shaft diameter should be 2.7m and 2.75m for L>20m and L<=20m respectively.
[1] ^ denoted As-Built Figure
[4] The estimated cost to be referred to the latest returned tenders.
