Minimal Time Consumption Constructing High-Rise Buildings

Optimal Time Utilization whilst Constructing Tall Buildings

Abstract:

The triangle of project objectives - cost, quality and time is well known. The relative priorities among them are established by the client/owner. Over the last three decades, special needs pertaining to construction of tall buildings have been established. Particular emphasis have been given to reducing construction schedules. Real estate costs, housing demands, and growth of major cities in developing countries have changes the core concept of traditional construction management and methods.

Being a contemporary civil engineer, I analyze the main factors influencing construction schedules of tall buildings and describing methods and measures that have been successfully used in achieving time reduction in overall construction schedule.

Background:

Time over-runs in construction projects have often been one of the more remarkable 'failure modes' drawing criticism on construction industry. Resulting in overheads incurred by all participants,as well as potential claims for progress disruptions by contractors, and/or liquidated damages by clients are the most common consequences.

 There is a global competitiveness going on to improve such failures of time lag.

Management Method

Project Planning and Management:

                                                            The major activities in the construction of tall buildings generally are classified into the following packages:-

1. Site set-up.Activities necessary to establish temporary facilities at the work place and prepare the site for subsequent activities, including site layout.
2. Pilling.Activities  necessary to complete the groundwork up to but excluding ground floor slab, as well as foundations, under slab drainage, basement etc.
3. Pile caps/raft.Activities necessary to construct pile caps in the case of pile foundation, or the raft foundation, including the ground floor slab.
4. Superstructure.Activities necessary to erect the load bearing frame starting from the ground floor column/wall element, upto and including the main roof and upper roof, as well as pre-cast facade installation.
5. Electrical & Mechanical (E&M)services.Activities necessary to install the E&M works including electrical, fire services, elevators, water pump and water supply system, waste water system, telephone system, storm water drainage, lighting protection etc.
6. Finishes.Activities necessary to complete the building including any brickwork for internal partitions, plastering and tiling, carpentry and joinery, ironmongery, steel and metal works, glazing , painting, window installation, wall finishes etc.
7. External works. Other works adjacent to the building including underground cable ducts and drainage, covered walkways, planters, access roads, paving ,play areas, pavillion etc.

The duration of construction is the time span from beginning of foundation to completion and handover of building to client.The total schedule can be determined based upon the duration of the above phases

As common duration for tasks will be established. Contractors and managers knows how long it will take to drill and pour piles, what equipment to use, and so forth. they also know how to reduce this time through the controls of some variables in present.As once a better time ti perform an activity is achieved, there is both the challenge and competence to do it better next time.

Based on this knowledge, if the construction durations of every phase can be estimated reliably and objectively in the design stage, time uncertainty will be minimized in the construction stage.

In few newer studies the researchers found the 7 most important variables affecting the time schedule of tall structures are:

• Area of external cladding.
• Height of the building.
• Ratio of total gross area  to the number of stories.
• Type of foundation.
• Information flow between architect/engineer and contractors.
• Presence / absence of precast facade.
• Type of scheme(purchased/rental)

Managers are or to be alerted to the relevance of these factors whenever they have time constraints. The more accurate the information about these areas, the more reliable are the schedules.

These variable also inturn have influence on other factors such  as:-

1. The duration of piling works is related to piling cost, type of foundation and depth of foundation excavations.
2. The time required for superstructure construction is affected by the height of the building, labor availability and the presence / absence of pre-cast facade
3. Durations for E&M services and finishes are dependent upon the 'critical' superstructure duration.
4. Both planned and actual overall construction durations are related to construction cost, presence/absence of pre-cast facade, type of scheme (rental/purchase) and height or number of stories of the building.

Effective communication between several groups and hierarchical levels involved in a project emphasizes the need for efficient method of information processing in the building industry. Speed of decision-making involving all project teams; both formal and informal communication between client and consultant & between consultant and contractor affects the duration of primary work packages for building projects. Therefore, to accelerate communication and decision making among all parties, appropriate overall organisational structures and information communication network system linking all project teams should be developed through out the whole life of the project. The roles and responsibilities of those involved should be defined clearly, and designated decision makers should be clearly identified.

In my research other studies conducted over the years around the globe indicate that while procurement and non-procurement related factors contribute to cost over-runs are mainly influenced by non-procurement variables such as project characteristics (e.g complexity level of design and construction requirements) and client representative characteristics.

Many studies of delays in various construction industries have elicited diverse sets of causative factors. Table below provide a comparative overview of a cross-section of such factors as identified by different researchers. It shows that 'material shortage or late material delivery' is the most frequently cited cause of delays followed by others variably.

A cross-section of  findings on the major factors causing delays in construction projects

Construction Process and Materials:

Jump Form System to Construct Concrete Core Walls:-
                                                                                             The use of a climbing formwork system( sometimes referred to as self-climbing or self-lifting) to construct core walls of high rise buildings is successful in contemporary times in reducing construction times, primarily because the process become repetitive through the whole height of the building.

explaining the working

Basically it consist of a frame constructed from structural steel members over the score wall. Steel panels are hung from this frame, some supported on rollers. After the concrete walls are poured, the framework is released and rolled back from the concrete face. Jacks then lift or climb the whole frame up one level. All the framework panels are attached to the frame. The whole process take one and a half hours. The mould are cleaned after lifted out of the finished units and then re-assembled.

The cycle continues normally four days. Faster times have been achieved

Climbing Formwork on a concrete Pier

• Pre-Fabrication of Elements:

Prefabrication of elements is another method that has been successfully used to save time in construction of tall buildings. The repetitiveness of many elements makes this process suitable and very effective. Walls, Staircases, External facades and Door sets are the common examples of prefabricated elements.

Components are manufactured units, made to pre-determined sizes, to be used in buildings.Dimensional coordination governs their design and use and governs  their design and use. For example a prefabricated standard staircase components with a rise of 266 cm will govern the floor to floor height of the building in which it is to be fixed.

Prefabricated wall panels will closely govern the story height and the length of the building.

The advantages of Prefabrication are many a few are as:

1. Mass production of Units

•            Automation of the manufacturing process can save labor and reduce price.
•            Designers can become familiar with the standard units and have ready access to details.

     2.  Reduction of cost and Construction time on site

•            Less work to be done on site.
•            Saving in the use of formwork on site.
•            Precast units can be erected in bad weather.

     3.  Construction over and under water

•            No or little formwork is required.
•            False work is not required.
•            Minimal disruption to traffic.

     4.  Solution to the problem of local resources and labor

•            Units can be produced thousand of miles away from site.

The advantages of Prefabrication are as:

1. A small number of units required may prove to be uneconomical.
2. Special connections such as special bearings to transmit the vertical and horizontal loads, can add cost to the system.
3. Water proofing at joints.
4. Transportation difficulties.
5. Need for cranes.

Construction Equipments:  

Facilitating horizontal and vertical movements is one of the main tasks in tall buildings construction that must be accomplished in order to develop a schedule that is effective and tight.

• Hoists
• Gondolas/Swinging stage
• Work platform
• Elevators
• Cranes
• Modern use of Robotics in construction ;where application was impossible and troublesome to great success

Conclusion and Recommendation:

The pace of  living has changed along with the evolution of cities of the world; economic factors increasingly are shaping the needs for the new millenium and the construction industry is responding by aiming to speed up building processes. High rise buildings are particularly important . Government, researchers and firms of different countries around the world are targeting their effort towards reducing time in construction of such structures.

Management method, construction process and materials, and construction equipments have been successfully used in reducing time in overall schedule of tall buildings.

Significant factors that have emerged with regard to applying management methods to reduce construction schedules of tall buildings are
(a) Project scope factors (actual cost, present/absence of precast facade, height and number of stories)
(b)Non scope factors such as speed of decision making involving all project teams, information flow         between consultant and contractor and informal communication between architect/engineer and            contractor.
other factors such as Jump form system, Prefabrication elements have taken over the past repetitiveness and used to good optimum use these times of construction along with the new equipments.
It is my belief that this trend will be intensified in the near future. It is hoped this paper will help initiate and contribute to continual improvement of schedule performance of construction industry.