©KEBS 201 8 — All rights reserved  1 
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                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   
KENYA STANDARD                                                                                                                                                                                                       
                    
1 
 
 
 
 
 
 
 
 
 
 
 
 
Building Design and Erection Using 
Prefabricated Concrete — Code Of 
Practice   
 
 
    Public Review Draft  2018 
 
 
 
 
 
 
 
 
 
© KEBS 20 18                       First Edition 20 18 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
  DKS 2798 : 201 8     
TECHNICAL COMMITTEE REPRESENTATION  
 
The following organizations were represented on the Technical Committee:  
1. Architectural Association of Kenya  
2. National Housing Corporation  
3. Sutech limited  
4. Consumer information netwo rk 
5. Ministry of land  
6. Bamburi Cement Limited  
7. National Construction Authority  
8. Motorways Construction  
9. KOTO housing  
10. Kenya Bureau of Standards — Secretariat  
 
 
 
 
 
 
 
 
REVISION OF KENYA STANDARDS  
 
In order to keep abreast of progress in industry, Kenya Standards shall be regularly reviewed. 
Suggestions for improvements to published standards, addressed to the Managing Director, Kenya 
Bureau of Standards, are welcome.  
 
 
 
 
 
 
 
 
© Kenya Bureau of Standards, 201 4 
 
Copyright. Users are reminded that by virtue of Section  25 of the Copyright Act, Cap. 12 of 2001  of 
the Laws of Kenya, copyright subsists in all Kenya Standards and except as provided under Section 
26 of this Act, no Kenya Standard produced by Kenya Bureau of Standards may be reproduced, 
stored in a retrieval  system in any form or transmitted by any means without prior permission in writing 
from the Managing Director . 
 
. 
 
 
 
 
 
 
 
 
 
                                                   
 
 
           
 
   
   
   
 
©KEBS 201 8 — All rights reserved  3 
  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Building Design and Erection Using  
Prefabri cated Concrete — Code Of 
Practice  
 
 
 
 
  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
KENYA BUREAU OF STANDARDS (KEBS)  
 
Head Office:  P.O. Box 54974, Nairobi -00200, Tel.: (+254  020) 605490, 602350, Fax: (+254 020)  
604031  
E-Mail: info@kebs.org,  Web:http://www.kebs.org  
 
Coast Region                                                                                                                                                       Lake Region                                                                                                                                                                      Rift Valley Region  
P.O. Box 99376, Mombasa -80100                                             P.O. Box 2949, Kisumu -40100                                                                               P.O. Box 2138, Nakuru -
20100  
Tel.: (+254  041) 229563, 230939/40                                 Tel.: (+254 057) 23549, 22396                                                                 Tel.: (+254 051) 210553, 
210555  
Fax: (+254  041) 229448                                                                                                            Fax: (+254 057) 21814   DKS 2798 : 201 8     
Foreword  
 
This Kenya Standard was prepared by the construction technology  Technical  Committee under the 
guidance of the Standards Pr ojects Committee and it is in accordance with the procedures of the 
Kenya Bureau of Standards.   
Prefabrication, though desirable for large scale building activities, has yet to take a firm hold in the 
country. Advantages of recent trends in prefabrication have been taken note of and also the hazards 
attended to such  construction. A few recommendations on the need to avoid ‘progressive collapse’ of 
the structure have been  included. This has become necessary in view of such collapses in the past. A 
specific p oint to be borne in mind, therefore, is the need to make the structure reasonably safe against 
such a collapse.  
Prefabricated constructions being comparatively a new technique, some of the essential requirements 
for the  manufacture of the prefabricated com ponents and elements are also included in this standard.  
Since the aim of prefabrication is to effect economy, improvement in quality and speed in  
construction, the  selection of proper materials for prefabrication is also an important factor in the 
popular ization of this technique.  
The use of locally available materials with required characteristics and those materials which, due to 
their innate  characteristics, like light -weight, easy workability, thermal insulation and non -
combustibility, effect economy  and improved quality, may be tried.  
It is possible to achieve or evolve aesthetically satisfying designs using prefabricated construction. A 
careful and  judicious handling of materials and use of finishes on a prefabricated building can help the 
designer a great deal  in ensuring that the appearance of the building is aesthetically appealing. The 
purpose of finishes and architectural  treatment is not only to give prefabricated buildings an individual 
character but also to affect  better performance  and greater  user satisfaction.  
A system  building approach in construction is an upcoming field as far as its development and use in 
the country  is concerned. Two aspects specifically to be borne in mind are the system to be adopted 
for the different categories  of bui ldings and the sizes of their components. Here the principle of 
modular co -ordination is of value and its use  is recommended.  
This standard has been brought out to provide necessary guidance for design and erection of such 
systems. In this  standard, an att empt has been made to prescribe general requirements applicable to 
all valid existing systems  using prefabricated concrete as also to accommodate any new such system 
introduced in the country in future.  
The design of prefabricated buildings should include provision for all installations of services and their 
required  piping, wiring and accessories to be installed in the building.  
 
 
 
 
 
 
 
 
 
 
 
 
 
   
 
©KEBS 201 8 — All rights reserved  5 
  
 
 
 
1. Scope  
This standard covers provisions regarding modular  planning, component sizes, prefabrication 
systems,  design considerations, joints and manufacture, storage,  transport and erection of 
prefabricated concrete  elements for buildings and such related requirements.  
 
2. Normative references  
The following referenced documents are indispensable for the application of  this document. For  dated 
references, only the edition cited applies. For undated references, the latest edition of the  referenced 
document (including any amendments) applies. Information on currently valid national  and 
international standards can be obtai ned f rom the Kenya Bureau of S tandards .  
 
 KS ISO 9883:1993  Performance Standards in building - Performance test for precast concrete floors - 
Behaviour under concentrated load.  
 
KS ISO 24153:2009  Random sampling and randomization procedures  
 
EC 4 Design o f concrete structures - Part 1 -1: General rules and rules for buildings  
 
National Annex to Eurocode 1 - Action on structures Part 1 -4 General actions - wind actions  
 
National Annex to Eurocode 8 - National Annex to Eurocode 1 - Action on structures Part 1 -4 General 
actions - wind actions  
 
National Annex to Eurocode 8 - Design of structures for earthquake  resistance - Part 1 General rules, 
seismic actions and rules for buildings  
 
 Design of structures for eathquake resistance - Part 1 General rules, seismic acti ons and rules for 
buildings  
 
3. Terms  
3.1.  
Authority Having Jurisdiction  
The authority which has been created by a statute and which, for the purpose of administering the 
Code, may authorize a committee or an official or an agency to act on its behalf; herein  after 
called the ‘Authority’.  
3.2. 
Basic Module  
The fundamental module used  in modular co -ordination, the size of which is selected  for general 
application to building and its components.  
 
NOTE — The value of the b asic module has been chosen as 300 mm for the ma ximum flexibility and convenience. The 
symbol for the basic module is M.  
3.3. 
Cellular Concrete  
The material consisting of an inorganic binder (such as lime or cement or both) in combination 
with a finely ground material containing siliceous material (such as sand), gas generating material 
(for example, aluminum powder), water and harmless additives (optional); and steam cured under 
high pressure in autoclaves.  
3.4. 
Component  
A building product formed as a  distinct unit having specified sizes in three dimensions.  KENYA STANDARD   DKS 2798 : 201 8     
3.5. 
Composite Members  
Structural members comprising prefabricated structural units of steel, prestressed concrete or 
reinforced concrete and cast in -situ concrete connected together in such a manner that they act 
monolithically.  
3.6. 
Increments  
Difference between two homologous dimensions of components of successive sizes  
3.7. 
Light -Weight Concrete  
concrete of substantially lower unit weight than that made from gravel or crushed stone.  
3.8. 
Module  
a unit of size used in dimensional coordination  
3.9. 
Modular Co -ordination  
dimen sional coordination employing the basic module or a multi -module.  
 
NOTE — The purpose of modular co -ordination are,  
a) to reduce the variety of component sizes produced; and  
b) to allow the building designer greater flexibility in the arrangement of compon ents.  
3.10.   
Modular Grid  
a rectangular coordinate reference system in which the distance between consecutive lines is the 
basic module or a multimodule. This multi -module may differ for each of the two dimensions of the 
grid. 
3.11.   
Multi -module  
a module whose size i s a select ed multiple of the basic module  
3.12.   
Prefabricate  
Fabrication of components or assembled units prior to erectio n or installation in a building  
3.13.   
Prefabricated Building  
the partly/fully assembled and erected building, of which the structural parts cons ist of 
prefabricated individual units or assemblies using ordinary or controlled materials, including 
service facilities; and in which the service equipment may be either prefabricated or constructed 
in-situ. 
3.14.   
Sandwich Reinforced Concrete Panels  
panels mad e by sandwiching an insulation material between two layers of reinforced concrete to 
act as insulation for concrete panels.  
3.15.   
Self-Compacting Concrete  
Concrete that is able to flow under its own weight and completely fill the voids within the 
formwork, even  in the presence of dense reinforcement without any vibration, whilst maintaining 
homogeneity without segregation.  
3.16.   
Shear Connectors  
Structural elements, such as anchors, studs, channels and spirals, intended to transmit the 
horizontal shear between the pr efabricated member and the cast in -situ concrete and also to 
prevent vertical separation at the interface.    
 
©KEBS 201 8 — All rights reserved  7 
 3.17.   
System  
It is a particular method of construction of buildings with certain order and discipline using the 
prefabricated components, tunnel form or l arge panel shutters which are inter -related in functions 
and are produced based on a set of instructions  
3.18.   
Unit 
Building material formed as a simple article with all three dimensions specified, complete in itself 
but intended to be part of a compound unit o r complete building. Examples are brick, block, tile, 
etc. 
     
4.  Precast and masonry wall s ymbols  
 
Masonry walling  
 
Precast walling  
5. Materials, Plans And Specifications  
5.1.Materials  
Use of materials for plain and reinforced concrete shall  satisfy the require ments of  EC4 part 
1-1. Connections and  jointing materials shall be in accordance with 9.3.  
5.1.1.  While selecting the materials for prefabrication, the following characteristics shall be 
considered:  
a) Easy availability;  
b) Light -weight for easy handling and tran sport;  
c) Thermal insulation property;  
d) Easy workability;  
e) Durability;  
f) Non -combustibility;  
g) Sound insulation;  
h) Easy assembly and compatibility to form a  complete unit;  
j) Economy; and  
k) Any other special requirement in a particular  application.  
5.2.Plans and Specifications  
The detailed plans and specifications shall cover the following:  
a) Such drawings shall describe the elements and the structure and assembly including all 
required data of physical properties of component materials. Material specific ation, age of 
concrete for demoulding, casting erection tolerance and type of curing to be followed.  
b) Details of connecting joints of prefabricates shall be given to an enlarged scale.  
c) Site or shop location of services, such as installation of piping, wirin g or other accessories 
integral with the total scheme shall be shown separately.  
d) Data sheet indicating the location of the inserts  and acceptable tolerances for supporting 
the prefabricate during erection, location and position of doors/windows/ventilators , etc, if 
any. 
e) The drawings shall also clearly indicate location of handling arrangements for lifting and 
handling of the prefabricated elements in a safe manner. The dimensions of the lift  hooks 
and the weight of the element must be provided Sequence of e rection with critical check 
points and measures to avoid stability failure during construction stage of the building.  
f) The drawings shall follow standard code/key of description of precast elements  
  DKS 2798 : 201 8     
6. Modular co -ordination, architectural treatment and finish es 
6.1.Modular Co -ordination  
The basic module shall be adopted. After adopting this,  further work is necessary to outline 
suitable range of multimodules with greater increments, often referred to as preferred 
increments. A set of rules as detailed below would  be adequate for meeting the requirements 
of conventional and prefabricated construction.  
 
These rules relate to the following basic elements:  
 
a)The planning grid in both directions of the horizontal plan shall be:  
1) 15 M for industrial buildings, and  
2) 3 M for other buildings.  
The centre lines of load bearing walls should preferably coincide with the gridlines.  
b)The planning module in the vertical direction shall be 2 .4m for industrial buildings and 
1.2m for other buildings.  
c) Preferred increments for sill h eights, doors, windows a nd other fenestration shall be 
0.9m . 
d)In the case of internal columns, the grid lines shall coincide with the centre lines of 
columns. In case of external columns and columns near the lift and stair wells, the 
grid lines shall coinci de with centre lines of the column in the topmost storey.  
. 
6.2.Architectural Treatment and Finishes  
Treatment and finishes have to be specified keeping in view the requirements of protection, 
function and` aesthetics of internal and external spaces and surfac es. While deciding the type of 
architectural treatment and finishes for prefabricated buildings, the following points should be kept 
in view:  
a) Suitability for mass production techniques;  
b) Recognition of the constraints imposed by the level of workmansh ip available;  
c) Possibility of using different types of finishes;  
d) Use of finishes and architectural treatment for the creation of a particular architectural  
character in individual buildings and in groups of buildings by the use of colour, texture, 
projections and recesses on surfaces, etc;  
e) Incorporation of structural elements like joists, columns, beams, etc, as architectural features 
and the treatment of these for better overall performance and appearance;  
f) Satisfactory finishing of surfaces; and   
g) Use of lightweight materials to effect economy in the structural system.  
 
Some of the acceptable methods of finishes integral  with the precasting are,  
a) concrete surface moulded to design/shape;  
b) laid -on finishing tiles fixed during casting;  
c) fin ishes obtained by washing, tooling; grinding, grooving of hardened concrete;  
d) exposed aggregates; and  
e) other integral finishes.  
 
7. Components  
7.1.The dimensions of precast elements shall meet the design requirements. However, the actual 
dimensions shall be t he preferred dimensions as follows  unless otherwise agreed between 
the engineer and the precaster : 
 
a) Flooring and Roofing Scheme — Precast slabs or other precast structural flooring units:  
1) Length — Nominal length shall be in  multip les of 300mm . 
2) Wi dth — Nominal width shall be in multiples of 300mm  
3) Overall thickness — Overall thickness shall be a minimum of  75mm and in incremental 
multiples of 25mm  
 
b) Beams  
1) Length — Nominal length shall be in multiples of 300mm  
2) Width — Nominal width shall b e 100mm with an incremental in multiples of 25mm. 
3) Overall depth — Overall depth of the floor zone shall be 150mm with an i ncremental in   
 
©KEBS 201 8 — All rights reserved  9 
 multiples of 25 mm. 
 
c) Columns  
1) Height — Height of columns for industrial shall be 1200mm  and other building 1200mm . 
2) Lateral dimensions — overall  lateral dimension or diameter of columns shall be 100mm  
with an incremental  multiples of 25mm .  
 
d) Walls  
Thickness — The nominal thickness of walls shall be in multiples of 75mm and 100mm . 
 
e) Staircase  
Width — Nominal wi dth shall be 900mm with additional multiples of 300mm . 
 
f) Lintels  
1) Length — Nominal length shall be 1200mm with incremental  multiples of 300mm . 
2) Width — Nominal width shall be in multiples of 100mm . 
3) Depth — Nominal depth shall be in multiples of 100mm . 
 
g) Sunshades eaves  Projections  
1) Length — Nominal length shall be in multiples of 1200mm . 
2) Projection — Nominal length shall be in multiples of 300mm . 
 
7.2.Casting Tolerances of Precast Components  
  DKS 2798 : 201 8     
 
 
8. Prefabrication Systems And Structural Schemes  
8.1.The word ‘system’ refers to a particular method of construction of buildings using the 
prefabricated components which are inter -related in functions and are produced to a set of 
instructions. With certain constraints, several plans are possible, using the same  set of 
components. The degree of flexibility varies from system to system. However, in all the 
systems there is a certain order and discipline.  
8.2.The following aspects, among others, are to be considered in devising a system:  
a) Effective utilization of spa ces; 
b) Straight and simple walling scheme;  
c) Limited sizes and numbers of components;  
d) Limited opening in bearing walls;  
e) Regulated locations of partitions;  
f) Standardized service and stair units;  
g) Limited sizes of doors and windows with regulated  positions;  
h) Structural clarity and efficiency;  
j) Suitability for adoption in low rise and high rise building;  
k) Ease of manufacturing, storing and transporting;  
m) Speed and ease of erection; and  
n) Simple jointing system.  
8.3.Prefabrication Systems  
The system of prefabricated construction depends on the extent of the use of prefabricated 
components, their materials, sizes and the technique adopted for their manufacture and use in 
building.  
8.3.1.  Types of Prefabrication Components  
The prefabricated concrete comp onents such as those given below may be used which shall 
be in accordance with relevant Indian Standards, where available:  
a) Reinforced/prestressed concrete channel unit,  
b) Reinforced/prestressed concrete slab unit,  
c) Reinforced/prestressed concrete bea ms,   
 
©KEBS 201 8 — All rights reserved  11 
 d) Reinforced/prestressed concrete columns,  
e) Reinforced/prestressed concrete hollow core slab,  
f) Reinforced concrete waffle slab/shells,  
g) Reinforced/prestressed concrete wall elements,  
h) Hollow/solid concrete blocks and battens,  
j) Precast planks  and joists for flooring and roofing,  
k) Precast joists and trussed girders,  
m) Light -weight/cellular concrete slabs/wall panels,  
n) Precast lintel and eaves , 
p) Large panel prefabricates,  
q) Reinforced/prestressed concrete trusses,  
r) Reinforced/prestress ed roof purlins,  
s) Precast concrete L -panel unit,  
t) Precast concrete double -T unit,  
u) Prefabricated brick panel unit,  
v) Prefabricated sandwich concrete panels,  
w) Precast concrete foundation, and  
y) Precast concrete staircase.  
 
There may be other types  of components which may be used with the approval of the 
Authority.  
 
NOTE — The elements may be cast at the site or off the site.  
 
8.3.2.  Open Prefabrication system  
There are two categories of open prefab system  depending on the extent of prefabrication 
used in the construction as given in 7.3.2.1 and 7.3.2.2.  
 
8.3.2.1.  Partial prefabrication system  
This system basically uses precast roofing and flooring components and other minor 
elements like lintels, eaves , kitchen sills in conventional building construction. The struc tural 
system could be in the form of in -situ framework or load bearing walls  
 
8.3.2.2.  Full prefabrication system  
In this system almost all the structural components are  prefabricated. The filler walls may be 
of brick/block  masonry or of any other locally available  material.  
 
8.3.3.  Large Panel Prefabrication System  
This system is based on the use of large prefab components. The components used are 
precast concrete large panels for walls, floors, roofs, balconies, staircases, etc. The casting of 
the components could be at the site or off the site.  
Depending upon the extent of prefabrication, this system can also lend itself to partial prefab 
system and full prefab system. Structural scheme with precast large panel walls can be 
classified as given in 7.3.3.1 to 7.3.3.3.  
 
8.3.3.1.  Precast walls  
8.3.3.1.1.  Based on the structural functions of the walls, the precast walls may be 
classified as:  
a) Load bearing walls;  
b) Non -load bearing walls; and  
c) Shear walls.  
8.3.3.1.2.  Based on construction, the precast walls may be classified as:  
a) Homogeneous walls — which could be solid, hollow or ribbed; and  
b) Non -homogeneous walls — these could be composite or sandwich panels  
 
8.3.3.1.3.  Based on their locations and functional requirements the precast walls may 
also be classified as:  
a) External walls, which may be load bearing o r non -load bearing depending 
upon the lay -out; these are usually non -homogeneous walls of 
sandwiched type to impart better thermal comforts; and   DKS 2798 : 201 8     
b)  Internal walls providing resistance against vertical loads, horizontal 
loads, fire, etc.; these are normally h omogeneous walls.  
8.3.3.2.  Precast floors  
8.3.3.2.1.  Depending upon the composition of units, precast  flooring units may be 
classified as:  
a) Homogeneous floors — which may be of solid slabs, cored slabs, ribbed or waffle 
slabs; and  
b) Non -homogeneous floors — which may be of  multi -layered units with combinations 
of light -weight concrete or reinforced prestressed concrete, with filler blocks  
8.3.3.2.2.  Depending upon the way the loads are transferred, the precast floors may 
be classified as one way, two way or cantilever systems:  
a) One way system transfers loads to supporting members in one direction 
only. The precast elements which come under this category are channel 
slabs, hollow core slabs, channels and ties system, light -weight/cellular 
concrete slabs, etc.  
b) Two way systems transf er loads in both the directions imparting loads on 
the four edges.  
The precast elements under this category are room sized panels, two way 
ribbed or waffle slab systems, etc.  
c) Cantilever components are supported on one edge or two adjacent edges 
and othe r ends without supports.  
8.3.3.3.  Staircase systems  
Staircase system may consist of single flights with inbuilt risers and treads in the element. 
The flights are normally unidirectional transferring the loads to supporting landing slabs or 
load bearing walls.  
8.3.4.  Box T ype Construction  
In this system, room size units are prefabricated and erected at site. Toilet and kitchen blocks 
may also be similarly prefabricated and erected at site.  
 
NOTE — This system derives its stability and stiffness from the box units which are formed by four adjacent walls. 
Walls are jointed to make rigid connections among themselves. The box unit rests on foundation which may be of 
conventional type or precast type . 
 
9. Design considerations and requirements  
9.1.Design Considerations  
The precast struc ture should be analyzed as a monolithic one and the joints in them designed 
to take the forces of an equivalent discrete system. Resistance to horizontal loading shall be 
provided by having appropriate moment and shear resisting joints or placing shear wal ls (in 
diaphragm braced frame type of construction) in two directions at right angles or otherwise. 
No account is to be taken of rotational stiffness, if any, of the floor -wall joint in case of precast 
bearing wall buildings. The individual components shal l be designed, taking into consideration 
the appropriate end conditions and loads at various stages of construction. The components 
of the structure shall be designed for loads in accordance with EC 1 part 4  and EC 8 part 1 . In 
addition, members shall be d esigned for handling, erection and impact loads that might be 
expected during handling and erection.  
 
9.1.1.  In some conventional forms of construction, experience has shown that the structures 
are capable of safely sustaining abnormal conditions of loading and r emaining stable 
after the removal of primary structural members. It has been shown that some forms of 
building structure and particularly some industrialized large panel systems have little 
reserve strength to resist forces not specifically catered for in the design. In the light of 
this, therefore, recommendations made in 8.1.2 to 8.1.9 should be kept in mind for 
ensuring stability of such structure.  
9.1.2.  Adequate buttressing of external wall panels is important since these elements are not 
fully restrained on both sides by floor panels. Adequate design precautions may be 
taken by the designer. Experience shows that the external wall panel connections are 
the weakest points of a precast panel building.  
9.1.3.  It is equally important to provide restraint to all load bea ring elements at the corners of 
the building. These elements and the external ends of cross -wall units should be 
stiffened either by introducing columns as connecting units or by jointing them to   
 
©KEBS 201 8 — All rights reserved  13 
 nonstructural wall units which in emergency may support the load. Jointing of these 
units should be done bearing in mind the need for load support in an emergency.  
9.1.4.  In prefabricated construction, the possibility of gas or other explosions which can 
remove primary structural elements leading to progressive collapse o f the structure shall 
be taken into account. It is, therefore, necessary to consider the possibility of 
progressive collapse in which the failure or displacement of one element of a structure 
causes the failure or displacement of another element and result s in the partial or total 
collapse of the building.  
9.1.5.  Provision in the design to reduce the probability of progressive collapse is essential in 
buildings of over six storeys and is of relatively higher priority than for buildings of lower 
height.  
9.1.6.  It is neces sary to ensure that any local damage to a structure does not spread to other 
parts of the structure remote from the point of mishap and that the overall stability is not 
impaired, but it may not be necessary to stiffen all parts of the structure against lo cal 
damage or collapse in the immediate vicinity of a mishap, unless the design briefs 
specifically requires this to be  done.  
9.1.7.  Additional protection may be required in respect of damage from vehicles; further, it is 
necessary to consider the effect of damag e to or displacement of a load -bearing 
member by an uncontrolled vehicle. It is strongly recommended that important structural 
members are adequately protected by concrete kerbs or similar method.  
9.1.8.  In all aspects of erection that affect structural design, i t is essential that the designer 
should maintain a close liaison with the builder/contractor regarding the erection 
procedures to be followed.  
9.1.9.  Failures that have occurred during construction appear to be of two types. The first of 
these is the pack of card s type of collapse in which the absence of restraining elements, 
such as partitions, cladding or shear walls, means that the structure is not stable during 
the construction period. The second is the situation in which one element falls during 
erection and lands on an element below. The connections of the lower element then 
give way under the loading, both static and dynamic, and a chain reaction of further 
collapse  is set up.  
9.1.9.1.  A precaution against the first form of failure is that the overall stability of a building 
shall be considered in all its erection stages as well as in its completed state. All 
joints that may be required to resist moments and shears during the erection stage 
only shall be designed with these in mind. Temporary works required to provide  
stability during construction shall be designed carefully.  
9.1.10.  To guard against the second form of failure, that is, the dropping of a unit during 
erection, particular attention shall be given to the details of all pre -formed units and their 
seatings to ensur e that they are sufficiently robust to withstand the maximum stresses 
that can arise from site conditions. Precast concrete construction generally shall be 
capable of withstanding the impact forces that can arise from bad workmanship on site.  
9.2.Design Requir ements for Safety Against Progressive Collapse  
9.2.1.  Prefabricated buildings shall be designed with proper structural integrity to avoid 
situations where damage to small areas of a structure or failure of single elements may 
lead to collapse of major parts of th e structure.  
The following precaution may generally provide adequate structural integrity:  
a) All buildings should be capable of safely resisting the minimum horizontal load of 1.5 
percent of characteristic dead load applied at each floor or roof level sim ultaneously 
(see Fig. 1).  
b) All buildings shall be provided with effective horizontal ties,  
1) around the periphery;  
2) internally (in both directions); and  
3) to columns and walls.  
c) All buildings of five or more storeys shall be provided with vertical ties. In 
proportioning the ties, it may be assumed that no other forces are acting and the 
reinforcement is acting at its characteristic strength.  
Normal procedure may be to design the structure for the usual loads and then carry out 
a check for the tie fo rces.   
  DKS 2798 : 201 8     
 
 
9.2.2.  Continuity and Anchorage of Ties  
Bars shall be lapped, welded or mechanically joined in accordance with  EC2 part 1 -1 and 
part1 -2. 
9.2.3.  Design of Ties  
9.2.3.1.  Peripheral ties  
At each floor and roof level an effectively continuous  tie should be provided within  1.2 m 
of the edge of the  building or within the perimeter wall (see Fig. 2).  
The tie should be capable to resisting a tensile force of  Ft equal to 60 kN or (20 + 4N) kN 
whichever is less, where N is the number of storeys (including basement).  
9.2.3.2.   
These are t o be provided at each floor and roof level in two directions approximately at right 
angles. Ties should be effectively continuous throughout their length and be anchored to the 
peripheral tie at both ends, unless continuing as horizontal ties to columns or  walls (see Fig. 
3). The tensile strength, in kN per metre width shall be the greater of  
 
 
where (gk + qk) is the sum of average characteristic  dead and imposed floor loads in kN/m2 
and lr is the   greater of the distance between the centre of columns,  frames or walls 
supporting any two adjacent floor spans in the direction of the tie under consideration. The 
bars providing these ties may be distributed evenly in the slabs (see Fig. 4) or may be 
grouped at or in the beams, walls or other appropriate positio ns but at spacings generally not 
greater than 1.5 lr. 
 
9.2.3.3.  Horizontal ties to column and wall  
All external load -bearing members such as columns and walls should be anchored or tied 
horizontally into the structure at each floor and roof level. The design force for the tie is to 
be greater of,  
 
a) 2 Ft kN or ls × Ft × 2.5 kN, whichever is less for a column or for each metre length if 
there is a wall. ls is the floor to ceiling height, in metre.  
b) 3 percent of the total ultimate vertical load in the column or wal l at that level.  
 
For corner columns, this tie force should be provided in each of two directions 
approximately at right angles  
 
9.2.3.4.  Vertical ties (for buildings of five or more storeys)  
Each column and each wall carrying vertical load should be tied continuou sly from the 
foundation to the roof level. The reinforcement provided is required only to resist a tensile 
force equal to the maximum design ultimate load (dead and imposed) received from any 
one storey.  
   
 
©KEBS 201 8 — All rights reserved  15 
 
 
NOTE — If there are cantilever slabs, supporting external cladding, projecting in front of the columns and these 
are more than 1.2 m, then the peripheral tie shall go in the slab.  
 
FIG. 2 position for peripheral tie  
 
 
 
NOTE — If the peripheral tie consists of bars in an edge beam, then the bottom bars i n the slabs will not be at 
the same level as the peripheral tie bars. It is suggested that either an additional bar be used for the peripheral 
tie or the internal tie bars be extended and anchored around the top bar in the beam.  
 
FIG. 3 anchoring of ties i n slabs  
 
In situation where provision of vertical ties cannot be done, the element should be 
considered to be removed and the surrounding members designed to bridge the gap.  
 
9.2.4.  Key Elements  
For buildings of five or more storeys, the layout should be checked  to identify key 
elements. A key element is such that its failure would cause the collapse of more than a 
limited area close to it.  The limited area defined above may be taken equal to 70 m2 or 15 
percent of the area of the storey, whichever is lesser.  
If key elements exist, it is preferable to modify the layout so that the key element is 
avoided.  
9.3.Bearing for Precast Units  
Precast units shall have a bearing at least of 100 mm on masonry supports and of 75 mm at least 
on steel or concrete. Steel angle shelf  bearings shall have a 100 mm horizontal leg to allow for a 
50 mm bearing exclusive of fixing clearance. When deciding to what  extent, if any, the bearing  DKS 2798 : 201 8     
width may be reduced in special circumstances, factors, such as loading, span, height of wall and 
provision of continuity, shall be taken into consideration.  
10. JOINTS  
10.1.  The design of joints shall be made in the light of their assessment with respect to the 
following considerations:  
 
a) Feasibility — The feasibility of a joint shall be determined by its load c arrying capacity in 
the particular situation in which the joint is to function.  
b) Practicability — Practicability of joint shall be determined by the amount and type of 
material required in construction; cost of material, fabrication and erection and the time for 
fabrication and erection.  
c) Serviceability — Serviceability shall be determined by the joints/expected behavior to 
repeated or possible overloading and exposure to climatic or chemical conditions.  
d) Fire rating — The fire rating for joints of pr ecast components shall be higher or at least 
equal to connecting members.  
e) Appearance — The appearance of precast components joint shall merge with architectural 
aesthetic appearance and shall not be physically prominent compared to other parts of 
struct ural components.   
10.2.  The following are the requirements of a structural joint:  
a) It shall be capable of being designed to transfer the imposed load and moments with a known 
margin of safety;  
b) It shall occur at logical locations in the structure and at poin ts which may be most readily 
analyzed and easily reinforced;  
c) It shall accept the loads without marked displacement or rotation and avoid high local stresses;  
d) It shall accommodate tolerances in elements;  
e) It shall require little temporary support, permit adjustment and demand only a few distinct  
operation to make;  
f) It shall permit effective inspection and rectification;  
g) It shall be reliable in service with other parts of the building; and  
h) It shall enable the structure to absorb sufficient en ergy during earthquakes so as to avoid 
sudden failure of the structure.  
10.2.1.  Precast structures may have continuous or hinged connections subject to providing 
sufficient rigidity to withstand horizontal loading. When only compressive forces are to 
be taken, hin ged joints may be adopted.  
In case of prefabricated concrete elements, load is transmitted via the concrete. When 
both compressive force and bending moment are to be taken, rigid or welded joints may 
be adopted; the shearing force is usually small in the c olumn and can be taken up by 
the friction resistance of the joint. Here load transmission is accomplished by steel 
inserted parts together with concrete.  
10.2.2.  When considering thermal shrinkage and heat effects, provision of freedom of 
movement or introduction of restraint may be considered.  
10.3.  Following connections and jointing techniques materials may be employed:  
a) Welding of cleats or projecting steel,  
b) Overlapping reinforcement, loops and linking steel grouted by concrete,  
c) Reinforced concrete ties all ro und a slab,  
d) Prestressing,  
e) Epoxy grouting,  
f) Cement/Lime grout with non -shrink additive,  
g) Polymer slurry grouting at dowel cast joint bolts and nuts connection,  
h) Rebar fastener, chemical fastener and expansion fastener,  
j) Reinforcement coupler,  
k) A combination of the above, and  
m) Any other method proven by test.  
11. Tests for components/structures  
11.1.  Sampling Procedure  
11.1.1.  Lot 
All the precast units of the same size, manufactured from the same material under similar 
conditions of production shall be groupe d together to constitute a lot.  
The number of units to be selected from each lot for dimensional requirements shall depend   
 
©KEBS 201 8 — All rights reserved  17 
 upon the size of the lot and shall be in accordance with col 2 and col 3 of Table 1. The units 
shall be selected from the lot at rand om. In order to ensure the randomness of selection, 
reference may be made to  KS ISO 24153:2009 . 
11.1.2.  Number of Tests and Criteria for Conformity  
All the units selected at random in accordance with col 2 and col 3 of Table 1 shall be 
subjected to the dimensional  requirements. A unit failing to satisfy any of the dimensional 
requirements shall be termed as defective. The lot shall be considered as conforming to the 
dimensions requirements, if no defective is found in the sample, and shall be rejected, if the 
numbe r of defectives is greater than or equal to the first rejection number. If the number of 
defectives is less than the first rejection number the second sample of the same size as taken 
in the first stage shall be selected from the lot at random and subjecte d to the dimensional 
requirements. The number of defectives in the first sample and the second sample shall be 
combined and if the combined number of defectives is less than the second rejection number, 
the lot shall be considered as conforming to the dime nsional requirements, otherwise not.  
The lot which has been found as satisfactory with respect to the dimensional requirements 
shall then be tested for load test. For this purpose one unit shall be selected for every 300 
units or part thereof. The lot shal l be considered as conforming to the strength requirement, if 
all the units meet the requirement; otherwise not.  
 
11.2.  Testing on Individual Components  
The component should be loaded for 1 h at its full span with a total load (includ ing its own self 
weight) of 1.25 times the sum of the dead and imposed loads used in design. At the end of this 
time it should not show any sign of weakness, faulty construction or excessive deflection. Its 
recovery 1 h after the removal of the test load s hould not be less than 75 percent of the maximum 
deflection recorded during the test. If  prestressed, it should not show any visible cracks up to 
working load and should have a recovery of not less than 85 percent in 1 h.  
11.3.  Load Testing of Structure or Part  of Structure  
Loading test on a completed structure should be made, if required by the specification or if there 
is a reasonable doubt as to the adequacy of the strength of the structure.  
11.3.1.  In such tests the structure should be subjected to full dead load of  the structure plus an 
imposed load equal to 1.25 times the specified imposed load used in design, for a 
period of 24 h and then the imposed load shall be removed. During the tests, vertical 
struts equal in strength to take the whole load should be placed in position leaving a gap 
under the member.  
 
NOTE — Dead load includes self-weight  of the structural members plus weight of finishes and walls or partitions, if 
any, as considered in the design  
11.3.1.1.  If within 24 h of the removal of the load, a reinforced concre te structure does not 
show a recovery of at least 75 percent of the maximum deflection shown during 
the 24 h under load, test loading should be repeated after a lapse of 72 h. If the 
recovery is less than 80 percent in second test, the structure shall be d eemed to 
be unacceptable.  
11.3.1.2.  If within 24 h of the removal of the load, prestressed concrete structure does not 
show a recovery of at least 85 percent of the maximum deflection shown during 
the 24 h under load, the test loading should be repeated. The structu re should be 
considered to have failed, if the recovery after the second test is not at least 85 
percent of the maximum deflection shown during the second test.  
11.3.1.3.  If the maximum deflection, in mm, shown  during 24 h under load is less than 40 
L2/D, where l is  the effective span, in m; and D, the overall depth of the section, in 
mm, it is not necessary for the recovery to be measured and the recovery 
provisions of 10.3.1.1 and 10.3.1.2 shall not apply.  
 
 DKS 2798 : 201 8     
12. MANUFACTURE, STORAGE, TRANSPORT  AND ERECTION OF PRECAST EL EMENTS  
12.1.  Manufacture of Precast Concrete Elements  
12.1.1.  A judicious location of precasting yard with concreting, initial curing (required for 
demoulding), storage facilities, suitable transporting and erection equipments and 
availability of raw materials are the c rucial factors which should be carefully planned and 
provided for effective and economic use of precast concrete components in 
constructions.  The location shall adhere to the statutory requirement in the country  
12.1.2.  Manufacture  
The manufacture of the componen ts can be done in a factory for the commercial production 
established at the focal point based on the market potential or in a site precasting yard set up 
at or near the site of work.  
12.1.2.1.  Factory prefabrication  
Factory prefabrication is resorted to in a factor y for the commercial production for the 
manufacture of standardized components on a long -term basis. It is a capital intensive 
production where work is done throughout the year preferably under a closed shed to 
avoid effects of seasonal variations. High le vel of mechanization can always be 
introduced in this system where the work can be organized in a factory -like manner with 
the help of a constant team of workmen.  
12.1.2.2.  Site prefabrication  
In this scheme, prefabricated components are produced at site or near the  site of work as 
possible. This system is normally adopted for a specific job order for a limited period. 
Though there is definite economy with respect to cost of transportation, this system 
suffers from basic drawback of its non -suitability to any high de gree of mechanization and 
no elaborate arrangements for quality control. Normal benefits of continuity of work are  
not available in this system of  construction. Under this category there are two types that is 
semi -mechanized and fully -mechanized.  
12.1.2.2.1.  Semi -mech anized  
The work is normally carried out in open space with locally available labour force. The 
equipment machinery used may be minor in nature and moulds are of mobile or 
stationary in nature.  
12.1.2.2.2.  Fully -mechanized  
The work carried out under shed with skilled l abour. The equipments used are similar 
to one of factory production. This type of precast yards will be set up for the 
production of precast components of high quality, high rate of production.  
12.1.3.  The various processes involved in the manufacture of precast e lements may be 
classified as follows.  
12.1.3.1.  Main process  
a) Providing and assembling the moulds, placing reinforcement cage in position for reinforced 
concrete work, and stressing the wires in the case of prestressed elements;  
b) Putting concealed service condui ts/pipes;  
c) Fixing of inserts and tubes, where necessary (for handling);  
d) Pouring the concrete into the moulds;  
e) Vibrating the concrete and finishing;  
f) Curing (steam curing, if necessary); and  
g) Demoulding the forms and stacking the precast product s 
12.1.3.2.  Auxiliary process  
Process, such as the following, necessary for the successful completion of the processes 
covered by the main process:  
a) Mixing and manufacture of fresh concrete (done in a mixing station or by a batching 
plant);  
b) Prefabrication of re inforcement cage (done in a steel yard or workshop);  
c) Manufacture of inserts and other finishing items to be incorporated in the main precast 
products;  
d) Finishing the precast products; and  
e) Testing of products.  
12.1.3.3.  Subsidiary process  
All other works, suc h as the following, involved in keeping the main production work to a 
cyclic working:  
a) Storage of materials;  
b) Transport of cement and aggregates;    
 
©KEBS 201 8 — All rights reserved  19 
 c) Transport of green concrete and reinforcement cages;  
d) Transport and stacking the precast elements;  
e) Re pairs and maintenance of tools, tackles and machines;  
f) Repair and maintenance of moulds;  
g) Maintenance of curing yards; and  
h) Generation of steam, etc.  
12.1.4.  For the manufacture of precast elements all the above processes shall be planned in a 
systematic way  to achieve the following:  
a) A cyclic technological method of working to bring in speed and economy in 
manufacture;  
b) Mechanization of the process to increase productivity and to improve quality;  
c) The optimum production satisfying the quality control r equirements and to keep up 
the expected speed of construction aimed;  
d) Better working conditions for the people on the job; and  
e) Minimizing the effect of weather on the manufacturing schedule.  
 
12.1.5.  . The various stages of precasting can be classified as in Table 2 on the basis of the 
equipments required for the various stages. This permits mechanization and 
rationalization of work in the various stages. In the precasting, stages 6 and 7 given in 
Table 2 form the main process in the manufacture of precast con crete elements. For 
these precasting stages there are many technological processes to suit the concrete 
product under consideration which have been proved rational, economical and time 
saving. The technological line or process is the theoretical solution f or the method of 
planning the work involved by using machine complexes. Figure 5 illustrates 
diagrammatically  the various stages involved in a plant process.  
 
12.1.6.  The various accepted methods of manufacture of precast units can be broadly 
classified into two m ethods:  
a) The ‘Stand Method’ where the moulds remain stationary at places, when the various 
processes involved are carried out in a cyclic order at the same place, and  
b) The ‘Flow Method’ where the precast unit under consideration is in movement 
accordin g to the various processes involved in the work which are carried out in an 
assembly -line method.  
 
The various accepted precasting methods are listed in Table 3 with details regarding the 
elements that can be manufactured by these methods.  
  DKS 2798 : 201 8     
   
 
©KEBS 201 8 — All rights reserved  21 
 
 
12.2.  Preparation  and Storage of Materials  
Storage of materials is of considerable importance in the precasting industry, as a mistake in 
planning in this aspect can greatly influence the economics of production. From experience in 
construction, it is clear that there will  be very high percentages of loss of materials as well as poor 
quality due to improper storage and transport. So, in a precast factory where everything is 
produced with special emphasis on quality, proper storage and preservation of building materials, 
especially cement, coarse and fine aggregates, is of prime importance.  
12.3.  Moulds  
12.3.1.  Moulds for the manufacture of precast elements may be of steel, timber, concrete and 
plastic or a combination thereof. For the design of moulds for the various elements, 
special im portance should be given to easy demoulding and assembly of the various 
parts.  
At the same time rigidity, strength and watertightness of the mould, taking into 
consideration forces due to pouring of green concrete and vibrating, are also important  
12.3.2.  Toleranc es 
The moulds have to be designed in such a way to take into consideration the tolerances given 
in 6.2.  
12.3.3.  Slopes of the Mould Walls  
For easy demoulding of the elements from the mould with fixed sides, the required slopes 
have to be maintained. Otherwise ther e is a possibility of the elements getting stuck up with 
the mould at the time of demoulding.  
 
12.4.  Accelerated Hardening  
In most of the precasting factories, it is economical to use faster curing methods or artificial 
curing methods, which in turn will allow t he elements to be demoulded  much earlier permitting 
early re -use of the forms. Any of the following methods may be adopted  
  DKS 2798 : 201 8     
 
a) By heating the aggregates and water before mixing the concrete — By heating of the 
aggregates as well as water to about 70°C to  80° C before making the concrete mix and 
placing the same in the moulds, sufficiently high earlier strengths are developed to allow the 
elements to be stripped and transported.  
b) Steam curing — Steam curing may be done under high pressure and high temper ature in 
an autoclave. This technique is more suited to smaller elements. Alternatively, this could be 
done using low pressure steam having temperature around 80°C. This type of curing shall be 
done as specified in 11.5.2. For light weight concrete product s when steam cured under high 
pressure, the drying shrinkage is reduced considerably. Due to this reason, high  pressure 
steam curing in autoclave is specified for light weight low densities ranging from 300 to 1 000 
kg/m3. For normal (heavy) concretes as w ell as light weight concretes of higher densities, low 
pressure steam curing may be desirable as it does not involve using high pressures and 
temperatures requiring high investment in an autoclave (see also 11.5.2).  
c) Steam injection during mixing of conc rete — In this method low pressure saturated steam 
is injected into the mixer while the aggregates are being mixed. This enables the heating up 
of concrete to approximately 60° C. Such a concrete after being placed in the moulds attains 
high early strength . 
d) Heated air method — In this method, the concrete elements are kept in contact with hot air 
with a relative humidity not less than  80 percent. This method is specially useful for light 
weight concrete products using porous coarse aggregates.  
e) Hot wat er method — In this method, the concrete elements are kept in a bath of hot water 
around 50 °C to 80 °C. The general principles of this type of curing are not much different 
from steam curing.  
f) Electrical method — The passage of current through the concr ete panels generates heat 
through its electro -resistivity and accelerates curing. In this method, the concrete is heated up 
by an alternating  
 
12.4.1.  After the accelerated hardening of the above products by any of the above accepted 
methods, the elements shall be  cured further by normal curing methods to attain full   
 
©KEBS 201 8 — All rights reserved  23 
 final strength.  
12.4.2.  Accelerated hardening may also be achieved by the following techniques:  
a) Construction chemicals — Suitable construction chemicals may be used.  
b) Consolidation by spinning — Such a me thod is generally used in the centrifugal 
moulding of pipes and such units. The spinning motion removes excess water, effects 
consolidation and permits earlier demoulding.  
c) Pressed concrete — This method is suitable for fabrication of small or large prod ucts 
at high speed of production. A 100 -200 t press compresses the wet concrete in rigid 
moulds and expels water. Early handling and a dense wear resistant concrete is 
obtained.  
d) Vacuum treatment — This method removes the surplus air and water from the n ewly 
placed concrete as in slabs and similar elements. A suction up to about 70 percent of an 
atmosphere is applied for 20 to 30 min/cm thickness of the units.  
e) Consolidation by shock — This method is suitable for small concrete units dropped 
repeatedly from a height in strong moulds. The number of shocks required to remove 
excess water and air may vary from 6 to 20 and the height of lift may be up to as much 
as half the depth of the mould.  
12.4.3.  After the accelerated curing of the above products by any of the above accepted 
methods, the elements shall be cured further by normal curing methods to attain full 
final strength.  
12.5.  Curing  
12.5.1.  The curing of the prefabricated elements can be effected by the normal methods of 
curing by sprinkling water and keeping the elements  moist. This can also be done in the 
case of smaller elements by immersing them in a specially made water tanks.  
12.5.2.  Steam Curing  
12.5.2.1.  The steam curing of concrete products shall take place under tarpaulin in tents, 
under hoods, under chambers, in tunnels or in spe cial autoclaves. The steam shall 
have a uniform quality throughout the length of the member. The precast elements 
shall be so stacked, with sufficient clearance between each other and the 
bounding enclosure, so as to allow proper circulation of steam.  
Before the concrete products are subjected to any accelerated method of curing, 
the cement to be used shall be tested in accordance with relevant Indian 
Standards especially for soundness, setting time and suitability for steam curing.  
In the case of elements manufactured by accelerated curing methods, concrete 
admixtures to reduce the water content may be allowed to be used. The normal 
aeration agents used to increase the workability of concrete should not be allowed 
to be used. Use of calcium chloride based a dmixtures should not be used for 
reinforced concrete elements so as to meet the chloride limits prescribed in IS 
456. 
12.5.2.2.  The surrounding walls, the top cover and the floor of steam curing chamber or 
tunnel or hood shall be so designed as not to allow more tha n 1 kcal/m2/h/°C.  
12.5.2.3.  The inside face of the steam curing chamber, tunnel or hood shall have a damp -
proof layer to maintain the humidity of steam. Moreover, proper slope shall be 
given to the floor and the roof to allow the condensed water to be easily drained  
away. At first, when steam is let into the curing chambers, the air inside shall be 
allowed to go out through openings provided in the hoods or side walls which shall 
be closed soon after moist steam is seen jetting out.  
 
12.5.2.4.  It is preferable to let in steam at the top of the chamber through perforated 
pipelines to allow uniform entry of steam throughout the chamber.  
12.5.2.5.  The fresh concrete in the moulds should be allowed to get the initial set before 
allowing the concrete to come into contact with steam. The regul ar heating up of 
fresh concrete product from about 20 °C to 35 °C should start only after a waiting 
period ranging from 2 to 5 h depending on the setting time of cement used. It may 
be further noted that steam can be let in  earlier than this waiting period  provided 
the temperature of the concrete product does not rise beyond 35°C within this 
waiting period.  
12.5.2.6.  The second stage in steam curing process is to heat up the concrete elements, 
moulds and the surroundings in the chamber,  
a) in the low pressure steam c uring the airspace around the member is heated up  DKS 2798 : 201 8     
to a temperature of 75°C to 80°C at a gradual rate, usually not faster than 30°C/h 
(this process takes around 1 h to 1½ h depending upon outside temperature); and  
b) in the case of curing under high pressur e steam in autoclaves, the temperature 
and pressure are gradually built up during a period of about 4 h.  
12.5.2.7.  The third stage of steam curing is to maintain the uniform temperature and 
pressure for a duration depending upon thickness of the section. This may va ry 
from 3 h to 5½ h in the case of low pressure steam curing and 4 h to 7 h in the 
case of high pressure steam curing.  
12.5.2.8.  The fourth stage of steam curing is the gradual cooling down of concrete 
products and surroundings in the chamber and normalization of th e pressure to 
bring it at par with outside air. The maximum cooling rate, which is dependent on 
the thickness of the member, should normally not exceed 30°C/h.  
12.5.3.  In all these cases, the difference between the temperature of the concrete product and 
the outsi de temperature should not be more than 60°C for concretes up to M30 and 
75°C for concretes greater than M45. In the case of light weight concrete, the difference 
in temperature should not be more than 60°C for concretes less than M25. For 
concretes greater  than M50, the temperature differences can go up to 75°C.  
12.6.  Stacking During Transport and Storage  
Every precaution shall be taken against overstress or damage, by the provision of suitable 
packings at agreed points of support. Particular attention is directe d to the inherent dangers of 
breakage and damage caused by supporting other than at two positions, and also by the careless 
placing of packings (for example, not vertically one above the other). Ribs, corners and intricate 
projections from solid section sh ould be adequately protected. Packing pieces shall not discolour, 
disfigure or otherwise permanently cause mark on units or members. Stacking shall be arranged 
or the precast units should be protected, so as to prevent the accumulation of trapped water or 
rubbish, and if necessary to reduce the risk of efflorescence.  
12.6.1.  The following points shall be kept in view during stacking:  
a) Care should be taken to ensure that the flat elements are stacked with right side up. For 
identification, top surfaces should be c learly marked.  
b) Stacking should be done on a hard and suitable ground to avoid any sinking of support 
when elements are stacked.  
c) In case of horizontal stacking, packing materials shall be at specified locations and shall be 
exactly one over the other to avoid cantilever stress in panels.  
d) Components should be packed in a uniform way to avoid any undue projection of elements 
in the stack which normally is a source of accident.  
12.7.  Handling Arrangements  
12.7.1.  Lifting and handling positions shall be clearly defin ed particularly where these sections 
are critical. Where necessary special facilities, such as bolt holes or projecting loops, 
shall be provided in the units and full instructions supplied for handling. For the purpose 
of testing the bolts/hooks, bond stre ngth shall be the criteria for embedded bolts and 
bearing strength for through bolts. For bond strength, pull out test of concrete shall be 
carried out  
12.7.2.  For precast prestressed concrete members, the residual prestress at the age of 
particular operation of h andling and erection shall be considered in conjunction with any 
stresses caused by the handling or erection of member. The compressive stress thus 
computed shall not exceed 50 percent of the cube strength of the concrete at the time of 
handling and erecti on. Tensile stresses up to a limit of 50 percent above those specified 
in IS 456 shall be permissible.  
12.8.  Identification and Marking  
All precast units shall bear an indelible identification, location and orientation marks as and 
where necessary.  
The date of m anufacture shall also be marked on the units  
12.8.1.  The identification markings on the drawings shall be the same as that indicated in the 
manufacturer’s literature and shall be shown in a table on the setting schedule together 
with the length, type, size of the unit and the sizes and arrangement of all reinforcement.  
12.9.  Transport  
Transport of precast elements inside the factory and to the site of erection is of considerable 
importance not only from the point of view of economy but also from the point of view of desi gn 
and efficient management. Transport of precast elements must be carried out with extreme care 
to avoid any jerk and distress in elements and handled as far as possible in the same orientation   
 
©KEBS 201 8 — All rights reserved  25 
 as it is to be placed in final position.  
12.9.1.  Transport Inside the  Factory  
Transport of precast elements moulded inside the factory depends on the method of 
production, selected for the manufacture as given in Table 3.  
12.9.2.  Transport from Stacking Yard Inside the Factory to the Site of Erection  
Transport of precast concrete e lements from the factory to the site of erection should be 
planned in such a way so as to be in conformity with the traffic rules and regulations as 
stipulated by the Authorities. The size of the elements is often restricted by the availability of 
suitable  transport equipment, such as tractor -cumtrailers, to suit the load and dimensions of 
the member in addition to the opening dimensions under the bridge and load carrying 
capacity while transporting the elements over the bridge.  
12.9.2.1.  While transporting elements in various systems that is, wagons, trucks, bullock 
carts, etc, care should be taken to avoid excessive cantilever actions and desired 
supports are maintained. Transportation of prefabricated element should be done 
with safety ties and vibrations to the el ements in transit should be minimum. 
Special care should be taken at location of sharp bends and on uneven or slushy 
roads to avoid undesirable stresses in elements.  
12.9.2.2.  Before loading the elements in the transporting media, care shall be taken to 
ensure that the base packing for supporting the elements are located at specified 
positions only. Subsequent packings shall be kept strictly one over the other.  
12.10.  Erection  
In the erection of precast elements, all the following items of work shall be included:  
a) Slingin g of the precast element;  
b) Tying up of erection ropes connecting to the erection hooks;  
c) Cleaning of the elements and the site of erection;  
d) Cleaning of the steel inserts before incorporation in the joints, lifting up of the elements, 
setting them do wn into the correct envisaged position;  
e) Adjustment to get the stipulated level, line and plumb;  
f) Welding of cleats;  
g) Changing of the erection tackles;  
h) Putting up and removing of the necessary scaffolding or supports;  
j) Welding of the inserts, la ying of reinforcements in joints and grouting the joints; and  
k) Finishing the joints to bring the whole work to a workmanlike finished product.  
12.10.1.  In view of the fact that the erection work in various construction jobs using 
prefabricated concrete elements d iffers from place to place depending on the site 
conditions, safety precautions in the work are of utmost importance. Hence only those 
skilled foremen, trained workers and fitters who have been properly instructed about the 
safety precautions to be taken s hould be employed on the job. For additional 
information, see  Kenya Building Code   
12.10.2.  Transport of people, workers or visitors, by using cranes and hoists should be strictly 
prohibited on an erection site.  
In the case of tower cranes running on rails, the tra ck shall not have a slope more than 
0.2 percent in the longitudinal direction. In the transverse direction the rails shall lie in a 
horizontal plane.  
The track of the crane should be checed daily to see that all fish plates and bolts 
connecting them to the  sleepers are in place and in good condition.  
The operation of all equipment used for handling and erection shall follow the 
operations manual provided by the manufacturer. All safety precautions shall be taken 
in the operations of handling and erection  
For the design and construction of composite structures made up of prefabricated 
structural units and cast in -situ concrete, reference may be made to IS 3935.For design 
and construction of precast reinforced  concrete filligran  reference  may be made to  EC 4 
part 1 
For design and construction of floors and roofs using various precast units, reference 
may be made to KS ISO 9883:1993 , EC 2 part 1 -1  
For construction of floors and roofs with joists and filler blocks, reference may be made 
to  KS 2724:2017   
 
13. EQUIPM ENT 
13.1.  General   DKS 2798 : 201 8     
The equipment used in the precast concrete industry  construction may be classified into the 
following categories:  
a) Machinery required for quarrying of coarse and fine aggregates;  
b) Conveying equipment, such as belt conveyors, chain conveyors , screw conveyors, bucket 
elevators, hoists, etc;  
c) Concrete mixing machines;  
d) Concrete vibrating machines;  
e) Erection equipment, such as cranes, derricks, hoists, chain pulley blocks, etc;  
f) Transport machinery, such as tractor -cumtrailers, dumpers, Lorries, locomotives, motorboats 
and rarely even helicopters;  
g) Workshop machinery for making and repairing steel and timber moulds;  
h) Bar straightening, bending and welding machines to make reinforcement cages;  
j) Minor tools and tackles, such as wheel barrows, concrete buckets, etc; and  
k) Steam generation plant for accelerated curing.  
 
In addition to the above, pumps and soil compacting machinery are required at the building site 
for the execution of civil engineering projects involving prefabricated c omponents.  
Each of the above groups may further be classified into various categories of machines and 
further to various other types depending on the source of power and capacity.  
 
13.2.  Mechanization of the Construction and Erection Processes  
The various proces ses can be mechanized as in any other industry for attaining the 
advantages of mass production of identical elements which in turn will increase productivity 
and reduce the cost of production in the long run, at the same time guaranteeing quality for 
the e nd-product. On the basis of the degree of mechanization used, the various precasting 
factories can be divided into three categories:  
a) With simple mechanization;  
b) With partial mechanization; and  
c) With complex mechanization leading to automation.  
 
13.2.1.  In simple mechanization, simple mechanically operated implements are used to 
reduce the manual labour and increase the speed.  
13.2.2.  In partial mechanization, the manual work is more or less eliminated in the part of a 
process. For example, the batching plant for mix ing concrete, hoists to lift materials to a 
great height and bagger and bulldozer to do earthwork come under this category.1  
13.2.3.  In the case of complex mechanization leading to automation, a number of processes 
leading to the end -product are all mechanized to a large extent (without or with a little 
manual or human element involved). This type of mechanization reduces manual work 
to the absolute minimum and guarantees the mass production at a very fast rate and 
minimum cost.  
13.2.4.  For equipments relevant Kenya Standa rds.