COMMERCIAL HIGH RISE BUILDINGS-5

Elevator Car Groupings and Lobby Design

The vertical transportation of people within a high-rise building is significantly influenced by local fire regulations. Fire departments often mandate specific safety measures, such as the pressurization of lift lobbies or compartmentation to prevent the spread of smoke and fire. A separate fire lift, located within a fire tower, is typically required for use during emergencies, while other elevators are brought to a neutral position.

The designer must ensure that the lobby will not be used as a common or public thoroughfare at ground floor level. In multiuse buildings care should be taken to provide separately identified lobbies for each group of elevators with clear signage. As a general guide, the width of elevator lobby should be twice the depth of elevator cars it is servicing. 

Consideration should be given to various elevator car groupings to optimize efficiency and safety. The specific configuration will depend on the building's layout, occupancy, and usage patterns.

The design of elevator lobbies is crucial for ensuring smooth traffic flow and preventing congestion, especially during emergencies. Designers must ensure that the lobby is not used as a common or public thoroughfare, particularly at ground floor level. In multi-use buildings, it is essential to provide separately identified lobbies for each group of elevators, accompanied by clear signage to guide occupants. As a general guideline, the width of the elevator lobby should be approximately twice the depth of the elevator cars it services. This provides adequate space for people to wait and enter the elevators without obstructing the flow of traffic.

Staircases: The Backbone of Fire Safety

Staircases are paramount for safe evacuation during a fire. Depending on the distance between the farthest point of the floor plate and the nearest staircase, there should be at least two escape staircases in a building. This redundancy ensures that occupants can evacuate safely even if one staircase is compromised.

The staircases must be fire-protected or fire-compartmented in relation to the rest of the building, effectively acting as safe spaces where occupants can take refuge while evacuating. The location of these staircases, as required means of egress, often plays a decisive role in shaping the overall form of the building. Escape staircases are distinct from any ceremonial internal staircases that may be present.

In high-rise buildings, elevators are generally not considered 'legal exits' during fire emergencies. Firefighters typically bring all elevators down to the ground floor and utilize the designated fire lift for firefighting operations. Therefore, the building's staircases are critical components of its life safety system, making their number and location crucial design considerations.

Impact of Local Byelaws on Staircase Design

Local byelaws provide detailed specifications regarding exit requirements and the construction of exit enclosures. Several key points within these regulations have a significant impact on the design of staircases:

• Number of Exits: The minimum number of required exits is determined by factors such as occupancy type, floor area, and occupant load. Byelaws specify the required number of staircases to ensure adequate egress capacity.

• Travel Distance: Byelaws limit the maximum travel distance from any point on a floor to the nearest exit. This requirement influences the placement of staircases to ensure that all occupants can reach an exit within a reasonable distance.

• Staircase Width: The minimum width of staircases is dictated by the anticipated occupant load. Wider staircases are necessary to accommodate a larger number of people evacuating simultaneously.

• Fire Resistance Rating: Byelaws specify the required fire resistance rating for staircase enclosures, including walls, doors, and floors. This rating determines the amount of time the staircase can withstand fire exposure, providing occupants with a safe escape route.

• Enclosure Requirements: Staircase enclosures must be continuous from the highest floor to the ground level or a designated exit discharge point. The enclosure must be constructed of fire-resistant materials and be free of any openings that could compromise its integrity.

• Door Requirements: Doors leading into staircases must be self-closing and fire-rated to prevent the spread of smoke and fire. The doors must also swing in the direction of egress to facilitate rapid evacuation.

• Lighting and Signage: Adequate lighting and clear signage are essential for guiding occupants to and through staircases during emergencies. Emergency lighting systems must be in place to provide illumination in the event of a power failure.

• Ventilation: Staircases may require ventilation systems to remove smoke and heat during a fire. These systems can be either natural or mechanical and are designed to maintain a tenable environment for evacuating occupants.

The local byelaws go into great details about the exit requirement and the way, in which exit enclosures must be constructed, the following key points have a major impact on design: 

•  Total number of people in the building i.e. occupancy load determines the number of separate exits. 
•  The provision of fire escape exits that lead occupants to a safe area.
• Limitations on the maximum travel distance permitted to reach a fire protected exit enclosure. The provision of a choice of path to an exit and a choice of exit in case one is blocked. 

Toilets: 

The toilets are very often located within the service core especially in high rise buildings for ease of plumbing and accessibility to the vertical risers. The extent and number of male, female, executive and disable friendly facilities are calculated, following local codes and occupancy load. 

Shafts are very important from ventilation point of view as well as maintenance point of view. Minimum size of shaft, placement of pipes, access/entry to shaft for maintenance needs to be taken into account. 

Shafts

Shafts play a crucial role in toilet design, serving both ventilation and maintenance purposes. The minimum size of the shaft, the placement of pipes within it, and the provision of access points for maintenance personnel must be carefully considered. Adequate ventilation is essential to prevent the buildup of odors and maintain air quality. Easy access for maintenance is necessary to ensure the long-term functionality and hygiene of the toilet facilities.

Vertical Riser Ducts for E&M Services

The service core also houses vertical riser ducts for electrical and mechanical (E&M) services. These ducts are critical for distributing essential utilities throughout the building. Several key considerations must be addressed in their design:

The other essential items to be considered in the design of the service core are the vertical riser ducts for E&M services. As a rule, risers with 'wet' services should be physically separated, as should tele-communication riser ducts and those carrying electrical ducts. Floor to floor compartmentation is usually required between ducts that pass through holes in the floors of the riser cupboards, and should form part of the same compartmentation as the floor or surrounding lobby. The need for floor to floor compartmentation of services can be omitted if individual riser ducts act as fire compartments in their own right. This usually means a two-hour fire rating for ducts, including the doors. The materials for vertical E&M service risers should be non combustible with recommended fire rating. 

Refuge Area: 

An area of refuge is a location in a building designed to hold occupants during a fire or other emergency, when evacuation may not be safe or possible. Occupants can wait there until rescued or relieved by fire fighters. Refuge area is required in buildings of height more than 24m. The area of each Refuge area is 4% of the area it serves.

Area Calculation

The area of each refuge area is typically calculated as a percentage of the floor area it serves. A common requirement is that the refuge area should be at least 4% of the floor area it serves. For example, if a floor has an area of 1000 square meters, the refuge area on that floor should be at least 40 square meters. In commercial High rise building, the first refuge is provided every 24m and every 7Th floor above 24m. 

SKY LOBBY:

The sky lobby concept offers a compelling solution to the vertical transportation challenges in tall buildings. It involves dividing the building into distinct zones, each served by a dedicated bank of local elevators. These zones are connected by express elevators that travel directly to designated sky lobbies located at strategic points within the building.

Express Elevators: The High-Speed Connectors

Express elevators are designed for speed and efficiency, transporting passengers quickly between the ground floor and the sky lobbies. These elevators make limited stops, minimizing travel time for those heading to upper floors. By bypassing intermediate floors, express elevators significantly reduce congestion and improve overall elevator system throughput.

Sky Lobbies: Transfer Hubs

Sky lobbies serve as transfer hubs where passengers can switch between the express elevators and the local elevators serving their desired zone. These lobbies are typically designed as spacious and well-appointed areas, providing comfortable waiting spaces and clear signage to guide passengers to the appropriate local elevators.

Local Elevators: Serving Specific Zones

Local elevators operate within specific zones of the building, serving the floors within that zone. Because each zone has its own dedicated bank of local elevators, passengers experience shorter wait times and more direct access to their destinations. This localized approach to vertical transportation significantly improves the overall efficiency of the elevator system.

MECHANICAL FLOORS:

A mechanical floor is a floor in a high rise building that provides space for building systems. An extremely tall building may have multiple mechanical floors to accommodate all of its needs. These floors are usually not accessible via regular elevators and stairwells, because they contain sensitive systems.

A service floor , or mechanical level is a story of a high-rise building that is dedicated to mechanical and electronics equipment.

As a rule of thumb, skyscrapers require a mechanical floor for every 10 tenant floors (10%) although this percentage can vary widely.

Since nearly all elevators require machine rooms above the last floor they service, mechanical floors are often used to divide shafts that are stacked on top of each other to save space. 

the primary purpose of mechanical floors is heating, ventilation, and air conditioning, and other services. They contain air handling units, cooling towers (in mechanical penthouses), electrical generators, chiller plants, water pumps, communication and control systems and so on.

A building may twist or change shape at this floor, for instance, creating a visual distraction that works well with the different external appearance.