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Tuesday, September 24, 2013

Construction Sequence of MEP works in Buildings


Typical Construction Sequence for Mechanical / Electrical / Plumbing Works in High Rise Building


Grouping of MEP Fixes like PVC Electrical conduits in Slabs :

1. MEP 1st Fix - All Concealed Items/Pipe Sleeves in Verticals/Horizontals (Column/Slab)

2. MEP 2nd Fix - Stage 1: High Level MEP Works at False Ceiling
i) Fixing supports, installation of Firefighting, Chilled Water piping, drainage pipes, water supply(hot & cold), rain water, cable ladders, G.I Conduiting, AC ducting
ii) Pressure tests and insulations
iii) Installation of FCUs, water heaters
(Note: False Ceiling people will fix runners after the Stage 1 of MEP 2nd Fix)

3. MEP 2nd Fix - Stage 2: Clearance for False Ceiling People
i) Sprinkler droppers, AC duct droppers, flexible cable for light fixtures, fire stopping and identification works etc.
(Note: False Ceiling people will close ceiling tiles and MEP people will connect their diffusers in position on the ceiling tiles - too much coordination is required at this stage)

MEP 2nd Fix: Other Areas
Installation of all equipments like AHUs(Floor mounted), all pumps, heat exchangers(if any), bus bars, generators, water tanks etc.,

4. MEP Final Fix
Installation of Air terminals, sprinkler heads, wiring accessories, low current devices, CCTV, Public Address System (PAS), Isolators, fire fighting equipments(Hydrants), Sanitaryware, DBs, SMDBs & Dressing, SMA TVs, Structured Cabling, All Switch Points

External and other MEP works
i) Connections to Main lines of Govt. Authority, water supply, drainage, ETISALAT
ii) LV Room installations (MDBs, SMDBs, DBs)
iii) Installation of external piping, Manhole construction
iv) Installation of lightning protection, Backup System, Intercom System etc.,

Base Isolation and Vibration Control Systems



LRI (Lead Rubber Isolator) device
LRI (Lead Rubber Isolator) device

This is a base isolation device that has thin rubber sheets and steel sheets laminated in a circular form with a lead plug inserted in the center. This device is able to withstand loads, absorb seismic energy, dampen vibration during an earthquake, and then reset itself to the original position following the seismic event.
CLB (Cross Linear Bearing) device device
CLB (Cross Linear Bearing) device device

This is a load-sustaining device that moves smoothly in a horizontal direction. It can be used either with lightweight or heavy buildings and features a high bearing capacity against the pullout force.
Vibration damping walldevice
Vibration damping walldevice

This is a thin steel box with a steel plate inserted from the upper floor. 
It is fixed on the floor and filled with a viscous fluid. It has a simple 
structure and can be used to attenuate the vibration caused by wind,
earthquakes, and other movement-generating phenomena.
FLR (Flat Lead plug Rubber) device device
FLR (Flat Lead plug Rubber) device device

This is a damping device that consists of laminated rubber sheets with a lead plug inserted in the center. The area that the lead plug occupies is larger than that of the lead plug in the LRI device. Although it is small in size, it produces a large damping effect and is used to control the vibrations in a high-rise building caused by earthquakes.
Damping cylinder device
Damping cylinder device

This is a cylindrical attenuates device that dampens vibration by converting and expanding micromotion in an axial direction to rotational motion. The unit itself is small in size but very powerful and is used to attenuate vibrations, caused either by wind or earthquake, in structures ranging from high-rise buildings to steel towers
Suspended floor aseismic insulation
Suspended floor aseismic insulation

The floor is suspended from an upper structure to control
horizontal and vertical vibration. This approach has been adopted, 
for example, to construct the floor of an electron microscope room 
where the requirement is to control vibration with a precision of microns.
PSA
PSA

This is a viscous damping device designed to increase viscous resistance using a communicating tube. Because it has a pantographic mechanism, it produces a powerful damping effect and is able to attenuate not only microvibration but also earthquake motion.

Urban Underground Space - New Methods


JUC method
JUC method

This method is used to create one new tunnel branching off from another tunnel or to join one tunnel to another tunnel without constructing a vertical shaft. By using this method, the effects of tunnel renovation or excavation work on the surrounding environment can be significantly reduced and the work period also shortened at the same time. With this approach, special segments are installed in the tunnel to be worked on first so that tunnel branching or joining work can be done using ordinary shield machinery.
Furukawa Viaduct

P&PC segment method and ring lock segments

With the P&PC segment method, a prestress force is applied circumferentially or in the direction of the tunnel axis to bring installed segments into firm contact with each other thereby forming a solid tunnel structure. The P&PC segment method, which was developed to construct shield tunnels, is not only cost-efficient but also very effective for constructing tunnels in land subject to high inner water pressure or for tunnels that require high earthquake resistance (This method was awarded the Innovative Technique Award by the Japan Society of Civil Engineers.). Ring lock segments have tendons designed as guides to facilitate the tunnel member assembly process. Because they are made rigid so as to resist high inner water pressure, they are used as the lining for underground rivers, underground regulating reservoirs, shield tunnels, and so forth, to prevent floods from occurring in urban areas.
Dustless shotcrete method

With the dustless shotcrete method, the centrifugal force generated by a rotating disk (impeller) is used to blow shotcrete onto the wall of a tunnel. Because compressed air is not used, the amount of generated dust can be decreased down to between 1/20 to 1/30 of what is normally experienced and a good working environment can be maintained.


Backfill shield method and Re-cube mole method (for removing installed cables and pipes without excavating the ground)

In urban areas cables and pipes are densely laid in the underground spaces. Many of the tunnels that contain these cables and pipes are becoming superannuated requiring renovation or replacement as they reach the limits of their capacity. Using the backfill shield method, the ground close to an existing tunnel can be excavated using backfill shield machinery while at the same time earth can be filled back into the existing tunnel. Using the Re-cube mole method, a medium-or small-sized tunnel can be renovated using either the sheath pipe method, the pullout method, the crushing method, or a combination thereof.

High Rise Building Construction - New Techniques

"MiFT200"-a next-generation construction method for high-rise housing

MiFT200 is a new construction methodology that has made it possible to build collective housing rising to 200-meters or higher, the highest collective housing in Japan. Because collective housing constructed with this approach has an SI (Skeleton Infill) structure, a high level of structural durability and earthquake resistance can be realized. Features of high-rise housing built with MiFT200 are an astylar living space (a large space without columns), free planning, flexible renovation, and so forth.
"CWIWC (Controllable Wide Wall Column) method" - a high-rise tabular housing construction methodology
"CWIWC (Controllable Wide Wall Column) method"-a high-rise tabular housing construction methodology

The CWIWC construction method was originally developed by us. By using this approach, high-rise tabular collective housing with 20 or more floors can be constructed. The collective housing built using this technique is highly aseismic as the structure incorporates a quake-resistant wall transpiercing from the first floor to the top floor. This quake-resistant wall is made of high-strength concrete of 60N/mm2 and high-strength bars of 700N/mm2. Extensive structural tests conducted on the quake-resistant wall show that it has very high aseismic performance.
HI-DOC method
Start of construction of the building framework
on Feb 23, 2002

HI-DOC method
Completion of construction of the building framework
on Apr. 15, 2002 
HI-DOC method

The DOC method was originally developed to shorten a construction period whilst ensuring the same quality of work throughout processes. This approach has been further upgraded to the HI-DOC method. Specifically this approach adopts a new technique for joining pre-cast columns without using scaffolds, a supply chain management system for controlling products and members delivered to a construction site by the minute as well as other features. Using the new HI-DOC method, the framework for a condominium with 23 household units on one floor can be constructed in only four days. This method can of course also be used to construct office buildings, commercial buildings, and distribution facilities etc.
Inverted construction method
Inverted construction method

Using the inverted construction method, after completion of the ground floor, the basement can be worked on simultaneously with the first and higher floors. This approach increases the safety of working in the basement and also shortens the construction period. In addition, the number of required transport vehicles is reduced since it is not necessary to use temporary retaining materials, and the completed first floor reduces the noise of work being carried out in the basement so that disturbance in the neighbourhood is minimized.

STEPS FOR SAFE DESIGN AND CONSTRUCTION OF MULTISTOREY REINFORCED CONCRETE BUILDINGS - PART 2


2.5 Heavy Water Tanks on the Roof:

Heavy water tanks add large lateral inertia forces on the building frames due to the so called ‘whipping’ effect under seismic vibrations, but remain unaccounted for in the design. See the fall of such water tank in
Fig.10
Fig.10 - 5 storey R.C., collapse of open plinth, water tank at top dislocated (Bhuj)

Recommendation:-

All projected systems above the roof top behave like secondary elements subjected to roof level horizontal earthquake motions which act as base motions to such projecting systems. To account for such heavy earthquake forces, IS:1893-2002 (Part 1) provides in clause 7.12 that their support system should be designed for five times the design horizontal seismic co-efficient Ah specified in clause 6.4.2. Similarly any horizontal projections as the balconies or the cantilevers supporting floating columns, the cantilevers need to be designed for five times the design vertical co-efficient as specified in clause 6.4.5 of IS: 1893-2002 (Part 1)                                                                                                   

2.6 Lack of Earthquake Resistant Design:

Many buildings in Gujarat were not designed for the earthquake forces specified in IS:1893, which was in existence from 1962, revised in 1970, 1976 & 1984. The applicable seismic zoning in Gujarat had remained the same as adopted in 1970 version. It is the same even in 2002 version of IS:1893 (Part I).
Fig.11:- Lateral Strength of Building Frame
All the upper floors weak in long directions (Izmit, Turkey 1999)
Recommendation:-

It does not need emphasizing that all buildings including the multistoried buildings should be designed in accordance with IS: 1893 (Part 1) and IS: 4326 – 1993. The salient features of the design will be presented in Para 3.0 in this guide.

2.7  Improper Dimensioning of Beams & Columns: 
The structural dimensioning of beams and columns was inadequate in terms of provisions in IS: 13920-1993 and also for proper installation of reinforcements in Beam-Column joints as per IS: 456 and IS: 13920.
Fig.12:- Plan of Reinforcement in Beams & Columns

Recommendation:

The relative dimensions of beams & columns become very important in tall buildings from
the point of view of provision of longitudinal & transverse reinforcement in the members as well as the reinforcement passing through and anchored in the beam-column joints, permitting enough space for proper concreting and without involving any local kinking of the reinforcing bars. The practice of using small dimension columns like 200 or 230 mm and beams of equal width is totally unacceptable from the reinforcement detailing view point. Infact for permitting the beam bars passing through the columns, without any local bending then straightening (introducing kinks), the proper scheme would be to use wider columns than the beams. Minimum dimensions of beams and columns, also limiting aspect ratios of the two members, are specified in IS: 13920 which need to be adhered to.


2.8 Improper Detailing of Reinforcement:

In detailing the stirrups in the columns, no conformity appeared to satisfy lateral shear requirements in the concrete of the joint as required under IS 4326- 1976 and IS: 13920-1993. The shape and spacing of stirrups seen in collapsed and severely damaged columns with buckled reinforcement was indicative of non-conformity even with the basic R.C. Code IS: 456-1978.

Recommendation:

In respect of proper detailing of reinforcement in beams, columns, beam-column joints as well as shear walls, all the provisions in IS:13920 have to be carefully understood and adopted in design. The philosophy of over-design of beams in shear to force flexural hinge formation before shear failure, confining of highly compressed concrete in columns and the use of properly shaped shear stirrups with 135 degree hooks are some low-cost but extremely important provisions. For overall safety of the frame, design based on the concept of strong-column, weak-beam system should be adopted as far as practical. It may be mentioned that the full ductility details as specified in IS: 13920 permit the use of the High Reduction Factor R=5 which would make the design economical. But if such ductility details are not adopted, the Reduction Factor is permitted as only 3.0, which means that the design force will become 1.67 times the case when full ductile detailing is adopted which may indeed turnout to be more expensive and at the same time brittle and relatively unsafe (see fig.13).
Fig.13:- Detailing of reinforcement (Overlapping Hoops & Crosstie)



2.9 Short Column Detailing
In some situations the column is surrounded by walls on both sides such as upto the window sills and then in the spandrel portion above the windows but it remains exposed in the height of the windows. Such a column behaves as a short column under lateal earthquake loading where the shear stresses become much higher than normal length columns and fail in shear. (See fig. 14)

Recommendation:
To safe guard against this brittle shear failure in such columns the special confining stirrups should be provided throughout the height of the column at short spacing as required near the ends of the columns.
 
          Fig 1 4 - Damage to buildings due to short column effect on columns

3.      Some Important Codal Design Provisions:

In the last few years the author has had the opportunity of reviewing many reinforced concrete building designs prepared by well-established consulting companies as well as individual consultants and felt the need of preparing brief guidelines so that no important Codal provisions are missed out and the various design details for achieving better construction in the field and better ductile performance in the event of a great earthquake are ensured. Thus a safe and ductile building could be achieved.

3.1 Building Configuration

For achieving basic structural safety of buildings under postulated earthquake forces the first important requirement is that the building should be designed with symmetrical configuration both horizontally and vertically. In any case the seismic force resisting elements must be planned symmetrically about the centre of the mass of the building. IS:1893 (Part 1-2002) presents in detail in cl.7.1 the various types of irregularities which should be avoided as far as possible or corrected by planning the structural resisting elements. The present day requirements of large column free spaces inside can be met by designing strong frames on the periphery of the building so as to resist most of the horizontal design seismic forces and relieving the internal columns relatively from the earthquake forces. For this purpose shear walls may be provided in the building perimeter to increase the stiffness in both principal axes of the building as compared with the internal columns which could be designed basically for vertical loads.

3.2 Calculation of Loads

The loads will include the following:

(i)                 Dead Loads: These will include the weight of all components at each level, viz., roof including water tanks, Barsatis, Parapets, roof finishes, slabs, beams, elevator machine room etc. and including all plasters and surface cladding etc., and each floor level including fixed masonry or other partitions, infill walls, columns, slabs and beams, weight of stairs, cantilever balconies, parapets and plastering or cladding wherever used. The unit weights may be taken from IS:875 (Part 1) or ascertained from the manufacturer.

(ii)               Imposed Floor Loads: IS 875 (Part 2) deals with the imposed loads on roofs, floors, stairs, balconies, etc., for various occupancies. There is a provision for reduction in the imposed loads for certain situations, e.g. for large span beams and number of storeys above the columns of a storey. The earthquake code IS: 1893 (Part 1)-2002 permits general reduction in roof and floor imposed load when considering the load combination with the earthquake loading. But the two types of reductions, that is, in IS: 875 (Part 2) and IS: 1893 (Part 1) are not to be taken together.

3.3 The Earthquake Load:

For working out the earthquake loading on a building frame, the dead load and imposed load and weights are to be lumped at each column top on the basis of contributory areas. The imposed load is to be reduced as specified in IS: 1893 (Part1)-2002 for seismic load determination. Let us call them Wi at ith floor and Wn at the nth level at the roof level for a n-storey building. Hence the total load at the base of the building just above the foundation will be

n
W        = Σ i=1 W i + Wo

where Wo is the weight of elements in the ground storey.

3.4 Earthquake Resistant Design

Now the following steps may be taken:

(a) Estimate fundamental time period Ta using empirical expressions given in the Code IS: 1893-2002.

Ta = 0.075 H0.75, IS: 1893 Cl.7.6.1 for bare frame along each axis

Tax = 0.09h/d along x -axis IS: 1893 Cl.7.6.2 for frame with substantial infills Ta z = 0.09h/b, along z-axis, IS: 1893 Cl.7.6.2 for frame with substantial infills

where h is the height of the building and d and b are the base dimensions of the building along x and z axis respectively.

(b)   Calculate the design horizontal Seismic coefficient Ah

Now compute the fundamental time periods T/x and T/z for the bare frame along the two axes by dynamic analysis. These are generally found to be higher than Tax and Taz respectively.

The design horizontal coefficient Ah is given by

Ah = (Z/2). (I/R). (Sa/g)


Take Z for the applicable seismic zone
(IS: 1893
Cl.6.4.2),
Take I for the use importance of the building
(IS: 1893
Table 2),
Take R for the lateral load resisting system adopted
(IS: 1893
Table 7),

and take Sa/g for the computed time period values T/x, Tax , T/z and Taz with 5% damping coefficient using the response spectra curves IS: 1893 Fig 2 for the soil type observed. Thus four values of Ah will be determined as follows:-

In x-direction A/hx for T/x & Ahax for Tax

In z-direction A/hz for T/z & Ahaz for Taz

(c)    Calculate the total horizontal shear (the base shear) The design value of base shear VB

VB = Ah W

as per 1893 Cl.7.5.3.

For design of the building and portions thereof, the base shear corresponding to higher of Ahax and A/hx, similarly between Ahaz and A/hz will be taken as minimum design lateral force.

(d)   Seismic Moments and Forces in Frame Elements:

Calculate the seismic moments and axial forces in the columns, shears and moments in the beams by using the seismic weights on the floors/(column beam joints) through an appropriate computer software (having facility for using floors as rigid diaphragm and torsional effects as per IS: 1893:2002).

It may be performed by Response Spectrum or Time History analysis. The important point is that according to IS: 1893 Cl.7.8.2., the base shear computed in either of the dynamic method, say V/B shall not be less than VB calculated under Cl.7.5.3 using Ahax and Ahaz. If so, then all shears, moments, axial forces etc worked out under dynamic analysis will be increased proportionately, that is, in the ratio of VB/V/B.

(e)    Soft Ground Storey

It must be designed according to Cl.7.10 of IS: 1893-2002.


4. Method of Design

Structural design of various members has to be done by Limit State Method, as per IS 456-2000 for which the following load combinations should be used to work out the maximum member forces:-

Using


DL
for
DEAD LOAD
LL
for
LIVE LOAD
EQX
for
SEISMIC LOAD (X) DIRECTION
EQZ
for
SEISMIC LOAD (Z) DIRECTION


The load combinations for analysis and design will be taken as follows:

1.
(DL+LL)*1.5
8.
(DL-EQX)*1.5
2.
(DL+LL+EQX)*1.2
9.
(DL-EQZ)*1.5
3.
(DL+LL+EQZ)*1.2
10.
0.9DL+EQX*1.5
4.
(DL+LL-EQX)*1.2
11.
0.9DL+EQZ*1.5
5.
(DL+LL-EQZ)*1.2
12.
0.9DL-EQX *1.5
6.
(DL+EQX)*1.5
13.
0.9DL-EQZ*1.5
7.
(DL+EQZ)*1.5



The members (beams, columns, shear walls etc.) and their joints will be designed for the worst combination of loads, shears and moments.


MATERIALS:

a)      Cement: Ordinary portland cement conforming to IS 269 - 1976 shall be used along with fly ash after carrying out the design mix from approved consultant.

b)      Reinforcement: Cold twisted high yield strength deformed bars grade Fe 415 conforming to IS: 1786-1985, or preferably TMT bars of standard manufacturer e.g. TATA Steel, SAIL or equivalent shall be used.

The following grades of concrete mix may be adopted or as required for safe design:

(a) For RCC columns in lowest few storeys
:
M35
(b) For RCC columns in the middle few storeys
:
M30
(c) For RCC columns in the top few storeys
:
M25
(d)
For beams, slabs, staircase etc.
:
M20
(e)
For raft foundation
:
M 20 or 25
(f)
Max. Water cement Ratio
:
0.45
(g) Minimum cement content
:
300 kg/m3 of concrete.
(h) Admixtures of approved brand may be used as per mix design


CLEAR COVER TO ALL REINFORCEMENT:

For mild Exposure and fire rating of 1 hr. following clear covers may be adopted

(a) For foundation R.C.C.:

i)      Footings             :  60 mm.
ii)  Raft
:
60 mm.
(b) For columns
:
40 mm
(c) For Beams
:  25 mm or main bar dia. whichever is more.
(d) For Slab
:
20 mm.


4.1  Ductile Detailing

After designing the frame column-beam, shear walls and foundation by limit state theory as per IS: 456:2000, all details of longitudinal steel, overlaps, shear capacities, confining reinforcement requirements, stirrups and ties etc. shall be worked out using the provisions of IS: 13920-1993.

The drawings should clearly show all the adopted details.

5.  Concluding Remarks

In a nut-shell, the seismic safety of a multi-storeyed reinforced concrete building will depend upon the initial architectural and structural configuration of the total building, the quality of the Structural analysis, design and reinforcement detailing of the building frame to achieve stability of elements and their ductile performance under severe seismic lading. Proper quality of construction and stability of the infill walls and partitions are additional safety requirements of the structure as a whole. Any weakness left in the structure, whether in design or in construction will be fully revealed during the postulated maximum considered earthquake for the seismic zone in the earthquake code IS: 1893.

Acknowledgement:

The figures have been taken from various sources to suit the text message and are anonymously acknowledged.




Inspite of that, the structural designers ignored the seismic forces in design. It may also be stated that most buildings are designed against lateral load in the transverse direction. Hence they collapse in the longitudinal directions.

Proper arrangement of columns is shown in Fig. 11 which would give adequate seismic resistance along both axes of the building.