J.S. Daniel paper for high rise building construction cycle

CONTENT OF THE PRESENTATION: (ABOUT 80 SLIDES)

1- DEFINITIONS OF HIGH-RISE BUILDINGS (5 SLIDES)
2- EXAMPLES OF HIGH-RISE BUILDINGS (1 SLIDE)
3- EXAMPLES OF SKYSCRAPERS (2 SLIDES)
4- INTRODUCTION AND PURPOSE OF THE PRESENTATION (1 SLIDE)
5- FACTORS INVOLVED IN CONSTRUCTION CYCLE OF HIGH-RISE BLDGS
5.1- FORMWORK (21 SLIDES)
5.2- CONCRETE TECHNOLOGY (7 SLIDES)
5.3- STRUCTURAL SYSTEM (3 SLIDES)
5.4- CONSTRUCTABILITY (7 SLIDES)
5.5- RESOURCES (11 SLIDES)
5.6- ADVANCED TECHNIQUE (14 SLIDES)
6- CASE STUDIED (6 SLIDES)
7- SUMMARY & CONCLUSION (1 SLIDE)

High-Rise Building Construction Cycles
Author: Jihad S. Daniel

1- DEFINITIONS OF HIGH-RISE BUILDINGS

1.1- Basic Definition of High Rise Buildings

For the purposes of the Emporis Data Committee (Emporis is one of the world's largest property
resources and source of information about buildings around the world), a high-rise building is
defined as a building of 35 meters or greater in height, which is divided at regular intervals into
occupied levels. To be considered a high-rise building, an edifice must be based on solid
ground, and fabricated along its full height through deliberate processes (as opposed to
naturally-occurring formations).



1.2- General Definition of High Rise Buildings

A high-rise building is distinguished from other tall man-made structures by the following
guidelines:
• It must be divided into multiple levels of at least 2 meters height;
• If it has fewer than 12 such internal levels, then the highest undivided portion must not exceed
50% of the total height;

Indistinct divisions of levels such as stairways shall not be considered floors for purposes of
eligibility in this definition.
Any method of structural support which is consistent with this definition is allowable, whether
masonry, concrete, or metal frame. In the few cases where such a building is not structurally
self-supporting (e.g. resting on a slope or braced against a cliff), it may still be considered a
high-rise building but is not eligible for any height records unless the record stipulates inclusions
of this type.



1.3- Encyclopedic Definition of High Rise Buildings

A high-rise is a tall building or structure. Normally, the function of the building is added, for
example high-rise apartment building or high-rise offices.

High-rise buildings became possible with the invention of the elevator (lift) and cheaper, more
abundant building materials. Buildings between 23 m to 150 m high are considered high-rises.
Buildings taller than 150 m are classified as skyscrapers. The average height of a level is
around 4 m high, thus a 24 m tall building would comprise 6 floors.

The materials used for the structural system of high-rise buildings are reinforced concrete and
steel. Most American style skyscrapers have a steel frame, while residential tower blocks are
usually constructed out of concrete.



1.4- Definition as per various bodies

Although the exact definition is immaterial, various bodies have tried to define what 'high-rise'
means:

The International Conference on Fire Safety in High-Rise Buildings defined a high-rise as
"any structure where the height can have a serious impact on evacuation“.

The New Shorter Oxford English Dictionary defines a high-rise as "a building having many
stories".

Massachusetts General Laws define a high-rise as being higher than 70 feet (21 m).

Most building engineers, inspectors, architects and similar professions define a high-rise as
a building that's at least 75 feet (23 m).



1.5- Minimum Height of High Rise buildings and Tallest High Rise Buildings

The cutoff between high-rise and low-rise buildings is 35 meters. This height was chosen based
on an original 12-floor cutoff, used for the following reasons:
• Twelve floors is normally the minimum height needed to achieve the physical presence which
earns the name "high-rise";
• The twelve-floor limit represents a compromise between ambition and manageability for a
worldwide database.

Since height information on smaller buildings is usually not readily available, the twelve-floor
limit is still used in most areas covered by the websites belonging to The Emporis Network. A
building of fewer floors may only be included as a high-rise when its exact height is known. In
most cases, a city is considered to have a satisfactory listing of high-rise buildings when all
twelve-floor buildings are counted.


2- EXAMPLES OF HIGH-RISE BUILDINGS IN LEBANON

Marina Towers Grand Habtoor Hotel – Beirut Phenicia Hotel Towers - Beirut
& Four Seasons Hotel - Beirut


3- EXAMPLES OF SKYSCRAPERS

Location : Dubai Location : Dubai Location : Shanghai China Location : Kuala Lumpur Location : Dubai
Height : 321 Meters Height : 705 Meters Height : 1228 Meters Height : 452 Meters Height : 1050 Meters
Floors : 70 Floors : 160 Floors : 300 Floors : 88 Floors : 230
Built : 1999 To Be Completed : 2009 To Be Completed : 2020 Built : 1998 To Be Completed : 2010


3- EXAMPLES OF SKYSCRAPERS

Tallest Towers Projects in Middle East Views from the 134th floor of
Burj Dubai


4- INTRODUCTION AND PURPOSE OF THE PRESENTATION
4.1- Introduction of the Presentation

Rapidly-paced building construction is dictated by financing concerns. Building owners and
developers want to minimize the high interest rate construction loan time period and press
toward building completion so that the revenue can be realized (time is money).
In cast-in-place multi-storey concrete buildings a “typical floor” construction cycle of 5 to 7 days
per floor is easily achievable and 2 and 3 days cycling is not uncommon in some areas.

4.2- Purpose of the Presentation

The purpose of this presentation is to present state-of-the-art engineering information on rapid
cycle concrete methodology depending among the others on formwork, design load, concrete
compressive strength, modulus of elasticity, concrete curing time, construction data, structural
system, number of shifts, HSE regulations, construction team performance/productivity &
learning curve and advanced planning techniques.


5- FACTORS INVOLVED IN CONSTRUCTION CYCLE OF HIGH-RISE BUILDINGS

5.1 - FORMWORK



5.1 FORMWORK

5.1.1 - Introduction:

• The fast-paced construction cycle is achieved through teamwork among the trades
involved with the building superstructure. This team carries out a predetermined
sequence of synchronized activities. Before this team can function, however, mutual
agreement and understanding must be reached between the Formwork Contractor and
the Designer. The Designer must come to an understanding of how the Formwork
Contractor would like to use the newly completed segments of the structure to support
formwork for the next floors in the cycle. At the same time, the Formwork Contractor
must come to an understanding of what limitations the Designer has on the use of these
newly completed segments of the structure as supports for the formwork of the floors to
be cast.


5.1 FORMWORK
5.1.1 - Introduction:

• The process of finding the optimum formwork concept for a structure starts in the tender
phase. Often it is here that the real decisions on the cost-effectiveness of a construction
project are made. Intelligent formwork-planning software was made as a measure tool
for automatic formwork planning. These programs also support the design of special
formwork by AutoCAD® and extensive structural analyses and the preparation of bills of
materials for working out offers.

• Some of the High-Rise Buildings’ Projects call for highly specialized formwork solutions
and unique know-how. The Expertise for Automatic Climbing and Project Management
ensure reliability end to end, particularly in projects that demand the highest level of
scheduling, commercial and engineering expertise.

• Time-to-completion can be enhanced by choosing suitable formwork system which
move up the tower at all times and never have to be brought back to the ground.


5.1 FORMWORK
5.1.2 - Formwork Systems:

The most efficient construction coordination plan for a tall building is one that allows formwork
to be reused multiple times. Formwork systems used for rapid cycle construction can be
grouped into four general categories:

Conventional and Gang Systems: these systems may be hand set or panelized. Hand-set
systems usually consist of wood shores or shoring supporting plywood-decked shores or
shoring supporting plywood decked wood or Aluminum framing. Segments of deck forms can
also be made into ganged panels supported by pre-attached shoring frames.

Flying Truss Systems: these systems use steel or Aluminum trusses to support plywood-
decked wood or Aluminum framing. Adjustable vertical members support the trusses off a
previously cast deck. The truss-mounted forms are moved between casting positions by crane.



5.1 FORMWORK

5.1.2 - Formwork Systems:

Column-Mounted Shoring Systems: these systems are large deck panels with framing
members that span between in-place columns or bearing walls with no intermediate vertical
shoring. Brackets or screw jacks, anchored to the in-place columns or walls, support the panel
perimeter framing which is quite often structural steel beams. The panels are moved between
casting positions by crane.

Tunnel Form Systems: these systems are factory-made U-shaped steel forms which permit
casting of a slab and the adjacent supporting walls at the same time. When sufficient concrete
strength is developed, the forms are collapsed or telescoped and moved to the next placement
location.



5.1 FORMWORK
5.1.3 – Technical Formwork Definition:
For the purpose of this presentation, the following definitions apply:

o Shores: vertical or inclined support members designed to carry the weight of formwork,
concrete and construction loads above.

o Re-shores: shores placed snugly under a stripped concrete slab or structural member
after the original forms and shores have been removed from a large area, thus requiring
the new slab or structural member to deflect and support its own weight and existing
construction loads applied prior to the installation of the re-shores. It is assumed that the
re-shores carry no load at the time of installation. Afterward, additional construction
loads will be distributed among all members connected by re-shores.

o Backshores: shores placed snugly under a stripped concrete slab or structural member
after the original formwork and shores have been removed from a small area without
allowing the slab to deflect or support its own weight or existing construction loads from
above.


5.1 FORMWORK
5.1.4 – Casting Cycle:

The formwork systems most often employed in rapid cycle work are conventional and ganged
systems or flying truss systems. Both of these two systems transmit the weight of newly placed
concrete to the most recently cast floors below. For sake of comparison, consider a common
shore/re-shore cycle used in multistory construction. The interconnected assembly consists of
several slabs, one or two levels of shores and a number of sets of re-shores. One commonly
employed construction sequence involves four phases in each casting cycle (see figure 1).


5.1 FORMWORK

5.1.4 – Casting Cycle:

The first phase is casting of new floor. In the second phase, the lowest storey of re-shores are
removed. In the third phase, the lowest story of shores are removed. The fourth phase involves
installation of re-shores in the storey vacated in phase three. The combination of shores and re-
shores provided must be such that the applied construction loads (generated by the casting of a
new slab) do not exceed the capacity of the interconnected slabs or induce excessive
deflections. :


5.1 FORMWORK
5.1.5 – Two to Three Days Casting Cycle:

If a two or three day cycle is desired, a system of pre-shores, primary forms and shores is used.
The system allows fast cycling of some of the forms while maintaining adequate support of the
newly cast slabs. A critical consideration in a two or three day cycle operation involves stripping
of the forms for the most recently cast slab. This slab, being about 28 hours old, is already
supporting the next floor’s form load. It is imperative that all the shores under this slab not to be
slackened in one operation. Pre-shores are placed so that, during the stripping process, the 28
hour old slab will never have an unsupported span of more than 2.4m. In this method forms
above the pre-shores remain temporarily pinned. Two or three day cycle systems that use
dimension lumber framing usually require two or sometimes 21/4 sets of forms and about 8 to
10 levels of re-shoring.


5.1 FORMWORK
Two or three day cycles can also be achieved in flying truss systems. In some cases the truss
supported panels are limited to a 2.4m (8 feet) width and are set two foot clear side by side. The
0.6m (2 foot) clearance allows room for lines of permanent shores. Panels are alternately
lowered ad decks re-shored, thereby not exceeding the 2.4m (8 feet) clear span limit (see
figures 2 & 3).


5.1 FORMWORK

If a two or three day cycle is desired a system of pre-shores, primary forms and shores is use.
Principles of engineering mechanics are applied to assess the effects of the forming operations
on the strength and serviceability of the in-place construction. The key element of a re-shoring
analysis is the apportioning of the construction loads throughout the system of slabs
interconnected by shores and re-shores. How these loads will be distributed is for the most part
dictated by the particular shore replacement method to be employed. Assessment of the in-
place concrete strength development is critical.


5.1 FORMWORK
5.1.6 – Formwork Brand Names & Characteristics:
ALUMA System is providing the high performance, time saving Aluminize Flying Tables, which
will reduce the project’s floor-cycles from 10 to three days. This improved performance directly
impacts on costs by reducing crane time, equipment and labor. Aluminize Tables consist of
large 60 m2 tables used in a rolling movement application, weighing only 1,920 kg each.

MIVAN System is another Aluminum system formwork which provides rapid, high quality and
cost effective formwork solutions that most prestigious high-rise projects has been key to its
continued success in the market. Designed and manufactured from lightweight Aluminum
panels, the system can be used over 250 times, offering excellent cost efficiency and can be
erected by unskilled labor. The high strength-to-weight ratio of MIVAN System’s components
also avoids the need for usage of crane in the operation of the equipment on site, as each and
every component can be erected, dismantled and moved by hand, thus providing the main
contractor with further time and cost savings. The modular nature of the system’s components
and the simplicity in erection and dismantling of the equipment enhances labor productivity and
reduces operator training periods. It is widely recognized as one of the world’s fastest and most
versatile formwork systems, with a typical floor-to-floor construction cycle of just four days.

5.1 FORMWORK
5.1.6 – Formwork Brand Names & Characteristics:

DOKA System is both fast and can achieve the necessary high quality finish for any project
and safety of the system for project’s operatives, particularly for the external formwork, which is
also a key factor. DOKA supports the selection, planning and application of its formwork
systems with a range of services that prevent cost overruns for formwork utilized on site and
thus effectively ease the work of site managers
and foremen.

PERI System is one of the world’s largest manufacturers and suppliers of formwork, shoring
and scaffolding systems. PERI also offers its customers engineering, planning, formwork
software, rental service and logistics support.


Description ALUFORMWORK DOKA PERI
Frame 100% Aluminum YES YES YES

Form facing 100% Aluminum YES NO NO

Panel weight/m² 20kg 33kg 33kg

Number of frame re-uses 1000 300 300

Number of form-facing re-uses 1000 60-70 60-70

Thickness frame 5cm + 10cm + 10cm

Wall Key Liberation YES NO NO

Floor Key Liberation YES NO NO

3 in 1 modularity Panel YES NO NO

Easy face forming replace YES YES YES

Easy to understand for Traditional Workmen NO YES YES

Flexible system, easy to assemble and requires
very little working skill NO YES YES

Components are versatile and suitable for all
major applications NO YES YES

Gives high labor and material productivity YES YES YES

Minimum Quantity of items YES (0 waste) NO NO

Good quality of finish is achieved YES (better) YES YES

Accuracy YES (better) YES YES

Safe & Speedy Construction YES (better) YES YES

Cost (1 – High , 2- Medium, 3 – Low) 1 3 2


5.1 FORMWORK
5.1.7 – Cases Studied:
1st Case:

A High-Rise Building Project in Dubai was on schedule using DOKA formwork systems in a
seven day floor construction cycle. The ground and mezzanine levels will be utilized as offices
and retail outlets with a gymnasium, swimming pool and multi-purpose hall destined for the third
floor. By the fourth floor, the dimensions for the main tower are almost 37 m x 37 m to give a
typical floor area of 1,370 m2 up to the 12th floor. Here with the inclusion of a balcony on each
face, the area increases to almost 1,500 m2. At the 26th-floor a larger cantilevered balcony is
introduced up to the 36th floor for what are described as some of the largest floor area
penthouses in a project of this type in Dubai. Regardless of the balconies however, floors on all
levels remain ‘typical’ allowing the contractors to meet the critical 7-day cycle using DOKA 150F
climbing formwork system for the external walls by the 12th-floor.
At the same time as construction of the tower was underway and working two floors above, the
Contractor constructed the project’s central 13.5 m x 13.5 m core shaft to house five lifts and
two staircases; once again using the DOKA 150F climbing system.


5.1 FORMWORK
1st Case:
Throughout slab construction of the 36th storey tower, the
Contractor was using two sets of DOKAFLEX tables, each
covering 1,400 m2 approximately. As ready-assembled
units, the DOKAFLEX tables reduce the number of separate
items needed for each floor formwork. Pre-assembled table
forms are easily shifted in one piece to the next position to
be cast without being dismantled. With fewer separate
parts, formwork erection and striking are greatly
accelerated; ensuring shortest possible forming times for
the contractor.


5.1 FORMWORK
2nd Case:
Marina Towers - Beirut: The Luxury High-Rise Building comprises of a mix of post-tensioned
and conventional cover slabs starting from the first floor up to the 25th floor. The area of each
floor is approximately 1,050 m2 and comprises of a core shaft to house lifts, staircases and E/M
shafts. The concrete construction for each typical floor was as follows:

Vertical elements: Shuttering, reinforcement and pouring vertical elements: 3 days
Post-Tension cover slab:
● Shuttering, reinforcement, E&M embedment, Post-Tensioning tendons and pouring PT
cover slab: 5 days
● Stressing, post-tensioning cables of cover slab (3 days after pouring of PT slab): 1 day
Conventional cover slab: Shuttering, reinforcement, E&M embedment of the conventional
over slab and pouring: 6 days


5.1 FORMWORK
Therefore, using the DOKA formwork, the construction cycle
between one typical floor and the other was 9 days. The striking
shutter of cover slab and de-shuttering props of the PT slab was
done after stressing PT cables of the PT slab of the floor in
subject and the upper floor (1 day work). Also, the striking shutter
of the conventional cover slab and de-shuttering of props was
done after pouring of the conventional slab of the floor in subject and
the upper floor (1 day work). At the same time as construction of the
tower was underway and working two floors above, the Contractor
constructed the project’s central core’s walls using the DOKA 150F
climbing system with a 4.8m height of jump.

Therefore, the construction of the concrete core from the 1st service floor (above ground floor)
up to top of roof started on 02-Feb-04 and finished on 15-Jan-05 (about 1 year) when the slab
of the 1st service floor started on 18-Feb-04 and finished with the pouring of the last slab of top
of roof on 28-Feb-05 (also 1 year).


5.1 FORMWORK
3rd Case:

The Four Seasons Hotel - Beirut: The Hotel building has a total built-up area of 49,000 m2
allocated to below ground basement on 5 levels and a 110 meters High-Rise Tower (25 floors)
above ground and it is finished with flat roof containing swimming pool and various amenities for
hotel guests. This luxurious high-rise building was not designed with a central core including
lifts, staircases and E/M shafts and the concrete slabs are conventional ones. The Contractor
decided to divide each typical floor of 600 m2 of area (starting from the 4th floor) into 2 zones.
The concrete construction for each zone of each typical floor was as follows:
Vertical elements:
Shuttering, reinforcement and pouring vertical elements: 3 days
Conventional cover slab:
Shuttering, reinforcement, E&M embedment of the conventional over slab and pouring: 5 days


5.1 FORMWORK
3rd Case:
Therefore, using the DOKA formwork, the construction cycle
between one typical floor and the other was 8 days


5.2 CONCRETE TECHNOLOGY


5.2.1 – INTRODUCTION

Along with advances in the ways that concrete is brought to the site, the types of formwork in
which it is cured, and how it is placed at high elevations, its mechanical and chemical properties
have made great advances.

Building industry professionals are interested in increasing productivity by decreasing the
amount of time for concrete to reach its strength and the amount of material required to carry
the loads of a structure as well as have improved stability and toughness. It is well known that
time, money and labor costs together are a matter of great concern in the building industry.

This performance speeds the time for project completion and may reduce cost with the
reduction of waiting time and more reuse periods for formwork. Higher strengths that can be
achieved by High Performance Concrete (HPC) also add a few other beneficial effects to the
structure. These features of HPC make it appropriate for applications to high-rise buildings.


5.2.1 – CHARACTERISTICS OF HPC

HPC is a mixture which properties include increased strength and better performances in the
areas of durability, ductility, permeability, density, mixture stability and chemical resistance, to
name only a few. These will change depending on the type of admixture combined with
cement, aggregates and water for the final product. High-strength concrete is typically
recognized as concrete with a 28-day compressive strength greater than 42 MPa. More
generally, concrete with a uniaxial compressive strength and flexural strength greater than that
of moderate strength concrete. Strengths of up to 140 MPa have been used in different site
applications; where the most recognizable building with high strength concrete is the Twins
Petronas Towers Kuala Lumpur, Malaysia; which has concrete with strengths around 138 MPa.
Concrete strength enhancement can be achieved through use of admixtures to produce a low
water/cement ratio giving high performance concrete. These admixtures promote a high slump,
extremely flowable concrete that achieves high strengths while providing superior workability &
pump ability. They are also used for concrete requiring high-early stripping strengths.


5.2.1 – CHARACTERISTICS OF HPC

Once the high strength concrete is placed, the hardened concrete properties can be predicted
in addition to other special characteristics. Some of the properties slightly differ from concrete
with lower strength while some vary more significantly. In order to examine the performance of
high strength concrete in practice, several case studies can be investigated. However, during
the last decades high strength concrete has become more popular and researchers continue to
develop high strength concrete with better durability to harmful agents. "In general the primary
characteristics of high performance concrete can be summarized as workability, high early-age
strength, toughness, superior long-term mechanical properties, and prolonged life in severe
environment."


5.2.2 – ADVANTAGES & DISADVANTAGES OF HPC

High strength concrete resists loads that cannot be resisted by normal strength concrete.
Not only does high strength concrete allow for more applications, it also increases the
strength per unit cost, per unit weight, and per unit volume as well.
These concrete mixes typically have an increased modulus of elasticity, which increases
stability and reduces deflections producing concretes with higher compressive and flexural
strengths.


5.2.2 – ADVANTAGES & DISADVANTAGES OF HPC
Along with the inherent advantages of high strength concrete, several less clearly defined
disadvantages can materialize:
First, increased quality control is needed in order to maintain the special properties desired.
High strength concrete must meet high-performance standards consistently in order for it to
be effective.
Inspection in the field should be of high standards because if the contractor should decide to
change the mix design to improve workability, adding water for instance, the change will
diminish the properties of the concrete.
High quality materials must be used. These materials may cost more than materials of lower
quality; but "the economic benefits that can accrue from the use of high strength concrete
need not be overemphasized.
Consolidation is very important, high strength concrete needs to be compacted well.
Therefore high frequency vibrators are required. Under-vibration is of major concern
because these types of concretes usually are relatively stiff and contain little air.


5.2.2 – CONCLUSION

The ACI committee concluded that the use of high strength concrete outweighs the additional
expense. Higher economy can be obtained with high strength concrete rather than high strength
steel. High strength concrete may require special curing and placement requirements. Delays in
delivery and placing must be eliminated and sometimes it may be necessary to reduce batch
sizes if placing procedures are slower than anticipated.


5.3 - STRUCTURAL SYSTEM


5.3 STRUCTURAL SYSTEM

The issues involved with structural design and technology are ones of both natural and human
implications. A structure must be designed to carry gravity, wind, equipment and snow; resist
high or low temperatures and vibrations; protect against explosions; and absorb noises. Adding
to this the human factor means considering rentable spaces, owner needs, aesthetics, cost,
safety and comfort. Although one set is not mutually exclusive of the other, careful planning and
consideration are essential in an attempt to satisfy and integrate both.

Considering structure alone, there are two main categories for high-rise buildings-structures that
resist gravity and lateral loads and those that carry primarily gravity loads. Since skyscrapers
have the largest needs for resisting high magnitudes of wind, the lateral load resisting system
becomes the most important.


5.3 STRUCTURAL SYSTEM
5.3.2 – CONCRETE STRUCTURAL SYSTEMS
The concrete systems that are suitable for different ranges of number of stories are shown in
below figure. Shear walls, may be described as vertical, cantilevered beams, which resist lateral
wind and seismic loads acting on a building transmitted to them by the floor diaphragms.
Reinforced concrete's ability to dampen vibration and provide mass to a building makes it a
good choice of materials. These elements are a variety of shapes such as, circular, curvilinear,
oval, box-like, triangular or rectilinear. Many times, a shear wall exists as a core-wall holding
internal services like elevators, janitor's closets, stairwells and storage areas.


5.4 - CONSTRUCTABILITY


5.4 CONSTRUCTABILITY
5.4.1 – DEFINITION

Degree to which the integration of experience and knowledge in a construction process
facilitates achievement of an optimum balance between project goals and resource constraints.



The timely execution of a construction project is very important to the owner, who makes plans
and commitments on the basis of the project's anticipated completion date. Failure of design
professionals to consider how a builder will implement the design can result in scheduling
problems, delays, and disputes during the construction process. Constructability of design is a
subjective scale that depends basically on a number of interdependent project-related factors.
Many design firms have a formal (explicit) constructability program that is launched as early as
the conceptual planning stage of the project. This research examines design professionals'
efforts to pursue constructability and provides recommendations for performing constructability
reviews in an efficient and effective manner.



Construction technologies vary from region to region all over the world and high-rise building
designers have to adapt their scheme to local constructability methods.
Design criteria governing tall buildings are detailed by the relevant Codes applicable within a
specific locality. The design engineer's challenge is to create a structural system complying with
the mandatory guidelines and other functional and construction requirements of the building.
With buildings becoming leaner and taller, design for lateral loads on tall buildings is usually a
greater challenge. Lateral loads include wind and earthquake loads.


5.4.3 – CONSTRUCTABILITY IN HIGH-RISE BUILDINGS

Constructability is described as the extent to which a design of a high-rise building provides for
ease of construction yet meets the overall requirements of the Project.

It is an “attitude” that must prevail through:

Conceptual Planning
Design and Procurement
Field Operations

Constructability leads to some important benefits:


5.4.4 – BENEFITS OF CONSTRUCTABILITY IN HIGH-RISE BUILDINGS
If ease of construction is built into the design, the following directly support project management
objectives:

Construction planning is made easier
Both design and construction costs can be reduced
Likewise the construction schedule may be shortened
Better quality can be required and expected
More realistic commitments can be made to subsequent trades, and to
Earlier owner occupation

Indirect benefits of design-construction are more difficult to quantify, but nevertheless include
team collaboration, parties working for mutual benefit, transfer of expertise from other projects,
shorter learning curve, etc.


5.4.5 – EXAMPLE OF CONSTRUCTABILITY FACTORS IN HIGH-RISE BUILDINGS

o High-rise buildings can be constructed very quickly using post-tensioned concrete systems.
o Rapid floor construction cycles are achieved through the use of high early-strength concrete.
o The use of standard design details of the post-tensioned elements, minimum congestion of
pre-stressed and non-pre-stressed reinforcement, and earlier stripping of formwork can
significantly reduce the floor construction time.


5.5 RESOURCES


5.5- RESOURCES

One of the most important factors that contributed to the overall success a Project is the
familiarization and training of a skilled labor force with a unique forming system. This involves
other issues such as productivity, learning curve and management of resources. Minimizing
crane time or any other equipment is also a key to construction scheduling.


5.5- RESOURCES
5.5.2 – OBJECTIVES AND APPROACHES

The objectives in scheduling the floor cycle are to ensure smooth flows of resources and to
optimize the use of formwork and other materials. The floor area is usually divided into zones to
allow the labor force and formwork materials moving between zones. The preparation of the
floor construction cycle would therefore be a resources allocation exercise. However, the
process is complex and difficult when it is done manually. Floats are created deliberately in the
schedule to ensure the balance in resources and to provide buffers. It is noted that variations in
working periods have significant impacts on the time schedule. A planning study proves that a
saving of approximately 35% in time could be achieved when the working period is extended by
20%.


5.5- RESOURCES
5.5.2 – OBJECTIVES AND APPROACHES

In scheduling the floor construction cycle, a simple approach is to adopt a constant duration for
the construction of the typical floors. However, this always induces a false impression to site
personnel that the construction processes are simple and could be achieved easily. For the
construction of high-rise buildings, site planning including activity scheduling and site production
layout has to be reviewed and re-plan from time to time in practice as site conditions and
resources are dynamic and uncertain.

Another major challenge in delivering projects on time is :


5.5- RESOURCES
5.5.3 – AVAILABILITY OF RESOURCES

Availability of the required resources which must be provided when needed, in the required
quality, quantity and combination.

The unprecedented number of projects in the UAE and the region makes the availability of such
resources a challenge for successful project delivery. Those involved must carefully plan their
resource requirements before implementing a project.


5.5- RESOURCES
5.5.3 – AVAILABILITY OF RESOURCES

The project schedule plan is an essential tool. Each activity must be analyzed to determine the
type of resources required for executing the same. This could be in terms of man-hours for labor
resources, equipment hours for equipment and machinery, quantities of materials to be ordered
and installed, and others. Extreme care should be given in allocating resources in terms of
crews. Assigning resources individually might prove to be of no use in many cases (i.e. crane
without operator or steel fixer without reinforcing material). It provides the project team with the
ability to visualize the resource requirements during the project life and determine if the
availability limits are in line with requirements. If the resource plan depicts that the required
project resources are within the set availability limits, the project team must analyze what
alternative resources can replace these. If this continues to be an issue, additional resources
need to be brought in either by direct hire or outsourcing them to a third party. Should the
completion date of the project be adhered to, the resource leveling technique will optimize the
use of float time but without exceeding the project completion date.


5.5- RESOURCES
5.5.4 – TYPICAL REQUIREMENTS OF RESOURCES

This is a comparison in required number of resources in term of site team for same structural
system, area and quantity of concrete work but different construction casting cycle and number
of working shift.


5.5- RESOURCES

The required resources to achieve a cycle of 7 to 8 days for a floor area of 600 m2 in a two
shifts’ works are as follows:
Formwork Team: 1 foreman, 2 charge hands (or assistant foreman), 4 carpenters, 4 assistant
carpenters and 9 labors
Field Rebar Team: 1 foreman, 2 charge hands (or assistant foreman), 4 rebar placers, 4
assistant rebar placers and 9 labors.
Workshop Rebar Team: 1 foreman, 2 rebar cutters/benders and 4 labors.
HVAC/Plumbing Team: 2 HVAC/Plumbers, 2 assistants and 2 labors(1 day work before
inspection and placement of concrete)
Electrical Team: 2 Electricians, 2 assistants and 2 labors (1 day work before inspection and
placement of concrete)
Concrete placer/finisher: 1 foreman for casting, 1 charge hand, 2 placers, 4 finishers and 4
labors (1 day work for placement and finishing of concrete)


5.5- RESOURCES
The required resources to achieve a cycle of 4 days for a floor area of 600 m2 in a two shifts’
works are as follows:
Day 1 - place the floor forms:
Formwork Team: 1 foreman, 2 charge hands (or assistant foreman), 6 carpenters, 6 assistant
carpenters and 10 labors
Day 2 - place the slab reinforcing steel:
Field Rebar Team: 1 foreman, 2 charge hands (or assistant foreman), 6 rebar placers, 6
assistant rebar placers and 10 labors.
Day 3 – place E/M reservations and pour the slab:
HVAC/Plumbing Team: 3 HVAC/Plumbers, 3 assistants and 3 labors (half day work before
inspection and placement of concrete). Workshop Rebar Team: 1 foreman, 2 rebar
cutters/benders and 6 labors. Electrical Team: 3 Electricians, 3 assistants and 3 labors (half day
work before inspection and placement of concrete). Concrete placer/finisher: 1 foreman for
casting, 1 charge hand, 3 placers, 6 finishers and 6 labors (1 day and night work for placement
and finishing of concrete)

5.5- RESOURCES

Day 4 - erect the column reinforcing steel and pour the columns to the next floor:
Formwork Team: 1 foreman, 1 charge hand (or assistant foreman), 3 carpenters, 3 assistant
carpenters and 6 labors. Field Rebar Team: 1 foreman, 1 charge hand (or assistant foreman), 3
rebar placers, 3 assistant rebar placers and 6 labors. Workshop Rebar Team: 1 foreman, 2
rebar cutters/benders and 2 labors. Concrete placer/finisher: 1 foreman for casting, 1 charge
hand, 2 placers, 2 finishers and 4 labors (1 day and night work for placement and finishing of
concrete)


5.5- RESOURCES

In order to achieve a 3 days cycle for a floor area of 600 m2, we need to have a three shift work
with the previous case’s day 1 and day 2 combined into 1 day that means the cycle will be as
follows:
Day 1: Place the floor forms and place the slab reinforcing steel in 3 shifts
Day 2: Place the E/M reservations/embedded items, inspect and pour the slab in 2 shifts.
Day 3: Erect the column reinforcing steel and pour the columns to the next floor in 2 shifts
(allow 2 shifts that means 24 hours for concrete curing time of the slab before proceeding with
columns of the next floor).


5.6- ADVANCED TECHNIQUES


5.6- ADVANCED TECHNIQUE

The advanced techniques for Planning of High-Rise buildings which are besides using Planning
software like Primavera or Microsoft Project, are the model techniques. However the building up
of simulation models requires Planners to have a good knowledge of simulation. A network
based simulation has been used in this study. This simplifies the skills and knowledge required
for modeling a simulation network as general reproduction program can be difficult for general
users. Planners who have the knowledge in constructing critical path network and bar charts
could be able to use the model.


5.6.2 – APPROACH

The constructing of simulation network for modeling is similar to the critical path network using
the “Activity on Node” format except that loops are allowed to show the re-cycling of the
resources. During the simulation process, the activities may either in an active if the constraints
are met or otherwise in an idle mode.

Although only one floor cycle is shown in the network, it covers the activities in the four zones,
which are handled within the simulation procedure. The ten activities are scheduled in a
sequential order. Two loops are put out from the main network indicating the dependence
relationship between installation of pre-cast façade, the activities for wall construction and
crane-related activities. Normally a tower crane can only be installed for a building block owing
to both economic reasons and space availability. Therefore, the crane can only serve one
activity at one time and it is important to optimize the usage of a tower crane which is one of the
critical resources in high-rise building construction.


5.6.2 – APPROACH

A “Start” and “Stop” node is assigned in the network for controlling the numbers of simulation.
During the simulation process, activity boxes are attached with a colored spinning icons
showing their status. Resources shared by activities can be represented by graphics moving
between the activities boxes.


5.6.3 – METHODOLOGY

In order to optimize the duration of a floor cycle or to determine the daily schedule, modelers
can modify the duration of the activities to suit the site conditions. It has to point out that the
duration of the activities can be shortened or extended by increasing or decreasing the input
resources, mainly the human resources in concrete frame construction generally. Table 1 shows
the duration for the activities of a typical floor construction cycle.



In order to generate realistic results, the duration assigned for the simulation has taken into
account the effects on hoisting times due to variations in hoisting height. For example, the
hoisting and fixing of eight pre-cast facades takes about 50 minutes at the lower floors and 75
minutes at the upper. Planners can adjust the duration if they identify significant differences
between the original input and the actual site conditions. Alternatively, Planners can carry out
simple work study techniques on site to collect data for predicting the hoisting time. Apart from
modifying the duration to suit the dynamic site conditions, Planning Engineers can review the
effects of working hours for a working day to a floor cycle.



Examining any standard floor cycle, it is evident that there are idling times in the schedule. The
idling times are created for leveling the resources. However, manual resources leveling is
complex and difficult and optimum solution cannot be easily found. The numbers of working
hours for a working day can be input as a constraint in the model. In Lebanon, most of the
residential areas in Beirut are densely populated and the government has imposed stringent
noise control ordinance to restrict the working hours for using noisy construction plant and
equipment. The normal working period to which there is no restriction is between 7:00 a.m. to
7:00 p.m. On the other hand, the normal working hours for the building industry in Lebanon lie
between 7:00 a.m. and 4:00 p.m. (or between 8:00 a.m. and 5:00 p.m.) and in UAE the normal
working hours lie between 8:00 a.m. to 6:00 p.m. Any time beyond the normal working hours,
the trade workers need to be paid with an overtime allowance or extra money. It is vital to
minimize the labor costs while meeting the program of the Project.


5.6.4 – PLANNING AND “WHAT IF” ANALYSIS

Planning, being an iterative process, will require different scenarios for different purposes, such
as "what-ifs?", and this would be characteristic of CPM also. In this study of Jumeirah Lake
Tower, the JGC company has studied four working period scenarios which have been reviewed
by using the simulation model. The summary of the simulation results is shown in Table 2.


5.6.4 – PLANNING AND “WHAT IF” ANALYSIS

In the four scenarios, the first working period follows the industry normal working hour and
constant activity duration was used. The remaining scenarios have been tested with
probabilistic or random activity duration. The simulation results confirm that the first scenario is
working approximately on a 6-day cycle. However, it is noted that there are significant saving in
time when the durations of activities are varied. In the second scenario, there is a saving of
25.8% even the activities are scheduled within the normal working period. However when the
working period is extended by one hour in the third scenario, further decrease in time is
minimal. In the last scenario, the working period is extended by two hours, a further saving of
11.4% (a total saving of 37.2%) is produced. It means that the increase of the working hours by
20% is not effective since the labor costs will be increased by 40%. This is a typical time-cost
trade off problem when time is approaching to the crash time solution.


5.6.5 – FLOOR CYCLE SCHEDULE


5.6.6 – SIMULATION NETWORK
The typical construction floor cycle shown above in Figure 1 can be easily developed into a
simulation network in Figure 2.


5.6.6 – CONCLUSION

The above study provides alternatives for Planners to make decisions on initial scheduling and
subsequent updating and enables Planners to locate the upper limit of the floor cycle i.e.
approaching to the crash time solution. However, it is a general rule in planning that the normal
time should be used in the planning stage unless the project duration would have already been
overrun. An aggressive Project Manager may consider applying the second scenario in order to
shorten the frame construction of 62 days (i.e. 40 x [6.0 – 4.45]) without spending overtime
payments. If the project has occurred delays, a more drastic decision will be to extend the
working period by two hours as if in the fourth scenario. Therefore, when deciding the
appropriate floor cycle duration, Planners have to review the factors and the merits prior to
determine the strategies.


5.6.7 – APPLIED EXAMPLE

In the construction of a 42 storey building for Jumeirah Lake Towers, each floor (of 1,200 m2 of
area each) is divided into four zones. One set of steel wall form covering the quantity of one
zone and two sets of slab timber forms with each set covering the whole area of one floor are
used. In order to speed up the construction, precast facades and semi-precast slabs are
employed. The construction cycle aims at ensuring smooth and balanced resource allocations
between trade workers, concreting work and formwork installation. As a result the resources
rotate horizontally between zones at the same floor level and move upward to the upper floor in
the next cycle. Figure 1 shows the schedule of a typical 6-day floor construction cycle including
ten critical activities. The schedule is prepared assuming that the activities are carried out at
constant duration. However, the duration of activities varies due to factors such as supply of
materials, skill of workers, learning curves, weather and efficiency of plant and equipment.
On the other hand, material hoisting plays an important role in high-rise building construction.
As the building “grows”, the transportation time increases and thus extends the duration for the
crane-related activities.


6- CASE STUDIED

6.1 – INTRODUCTION

The Project consists of two 24-storey towers attached at the base with a central lobby, one six-
storey building that is joined to one of the towers, and a three level post-tensioned parking
garage. The buildings house 435 one- and two-bedroom apartments, penthouse apartments,
and a full-service health club with an Olympic-size lap pool. One of the most important factors
that contributed to the overall success of this project was the collaboration between the general
contractor, subcontractors, and design team that resulted in cost-effective and timesaving
solutions, as outlined below. Another critical element was familiarization and training of a skilled
labor force with a unique forming system.


6- CASE STUDIED

6.2 – STRUCTURAL SYSTEM

The overall plan dimensions of a typical tower floor are 30.8 m by 30.8 m, with spans varying
between 4.0 and 7.3 m. A conventionally reinforced 200-mm thick concrete slab was chosen for
the floor system. 610 mm square columns are used for the full height of the tower, with varying
amounts of reinforcing steel. The lateral force resisting system consists of 355 mm thick shear
walls in a 12.2 by 12.2 m core area, and 305-mm thick outrigger walls that extend from the core
walls to the exterior of the building. The outrigger walls, used to reduce the drift of the building,
are located between the 2nd to 4th, 13th to 15th, and 21st to 23rd floors. Normal weight
concrete with a specified compressive strength of 25 MPa is utilized for the framing members,
except for the columns and shear walls in the lower 8 floors which are 35 MPa.
The foundation consists of 355 mm by 355 mm pre-cast concrete piles with a 120 ton capacity.


6- CASE STUDIED

6.3 – DESIGN LOADS

The buildings are designed in accordance with the Local Building Code. It is important to note
that seismic forces governed the lateral design, with the seismic base shear equal to 3.5% of
the weight of the building. In addition to specifying concrete compressive strength, modulus of
elasticity has been specified for the concrete in several high-rise buildings. A higher modulus of
elasticity provides a stiffer structure which has less lateral deflection under wind loads.


6- CASE STUDIED

6.4 – CONSTRUCTION DATA

Four to five days was a typical cycle for each floor. The shear walls were constructed first, three
floors ahead of the slabs and columns. The walls were formed with the PERI Formworks
system. SKYDECK, the high-strength lightweight Aluminum slab formwork which was also
supplied by PERI, was used for the slabs. The SKYDECK allowed for removal of the form
panels and beams without removal of the shores, thereby eliminating the need to re-shore.
Strength accelerators were used in the concrete mix for the floor slabs in order to achieve 10
MPa within 24 hours. This strength was needed in order to allow safe stripping of the forms. To
achieve a four to five day cycle, seven levels of shoring would normally be required. The
structural engineer for the project, performed a finite element analysis of the floor slabs and
shoring and determined that only four levels of shoring would be needed. The engineers
assured the accuracy of the finite element analysis. Measurements obtained from load cells
located on judiciously chosen shoring members compared very closely to the results of the
analysis. The collaboration between the contractors and the structural engineer resulted in
significant savings in time and money.


6- CASE STUDIED

6.5 – CONSTRUCTION CYCLE

A typical cycle was as follows:

Day 1 - place the floor forms;
Day 2 - place the slab reinforcing steel;
Day 3 - pour the slab;
Day 4 - erect the column reinforcing steel and pour the columns to the next floor.

Minimizing crane time was key to construction scheduling. Time-to-completion was enhanced
due to the fact that the PERI systems move up the tower at all times and never have to be
brought back to the ground.


6- CASE STUDIED

6.6 – CONCRETE VERSUS STEEL FRAMING

An additional significant cost savings was realized by using the flat plat system, since the
underside of the slab was used as the finished ceiling for the floor below. By working closely
with the pre-cast concrete contractor, simplicity of formwork was further achieved by supporting
the pre-cast panels directly on the columns, thereby eliminating the need for perimeter edge
beams. The overall time-to-completion of the project was a clear advantage of the concrete
system. Excavation and pile driving began in late November of 1996, and both towers were
completed in October of 1997. The faster completion time translates into earlier tenant
occupancy, and, thus, an earlier return on the developer's investment.


7- SUMMARY AND CONCLUSION OF THE PRESENTATION

New delivery systems, changes in formwork, high-strength concrete, optimum skilled resources,
advanced planning techniques, planning skills, constructability, reasonable management, etc.
allow to achieve a rapidly paced construction of high-rise buildings in the most advantageous
way in cost and time. Choosing a structural system is very complex in today's market. The
challenge for engineers and architects today is to make all the systems work together to their
maximum capacity and create a habitable environment for the people within the built structure.


QUESTIONS ?


THANK YOU


J.S. Daniel paper for high rise building construction cycle

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