Telescopic Bleachers

Overview

Telescopic bleachers are retractable grandstands designed for gymnasiums, multipurpose facilities, and arenas where seating must be stored to open floor space during non-event operations. The system comprises eight independent folding row decks stacked in a scissor-like arrangement, driven by a central electric motor that extends and retracts the entire assembly in under a minute.

Unlike fixed risers, telescopic bleachers allow a gymnasium to operate as either a 5,000 square meter open facility for volleyball or basketball during the week, then convert to a 150-seat gathering area for assemblies or tournaments on demand. The electrical drive and safety interlocks eliminate manual labor and prevent unsafe configurations.

How it works

Seating Array Structure

Eight Seating Deck assemblies are connected by a Frame Base through a pantograph mechanism. Each deck is a independent unit with 10–18 Seat Slat aluminum extrusions mounted to a Deck Frame steel subframe.

The decks are hinged together along their outer edges using heavy-duty Hinge Pin clevis pins rated for 50 kN shear loads. The pantograph linkages (essentially a multi-bar mechanism with equal-length arms) force each deck to remain at a fixed angle relative to the one below it. When the bottom deck remains stationary and the next deck is pushed upward by the drive system, the pantograph geometry automatically angles the upper deck at the correct rise-over-run ratio (approximately 1:1 for 430 mm rise per 430 mm horizontal advance).

Deployment Mechanism

A 3 HP motor drives a 50:1 self-locking gearbox, which turns a Chain Drive roller chain. The chain engages a drawbar mechanism that extends the top deck outward and upward. As the top deck moves, the pantograph linkages force all underlying decks into the staircase configuration. The Drive Belt provides secondary power transfer for smoother engagement.

The self-locking worm gear ensures that if the motor loses power mid-deployment, the bleachers remain exactly where they are; gravity alone cannot collapse them. This passive safety feature eliminates the need for active brakes except at parking positions.

Safety and Controls

The Control Unit houses a Siemens S7-1200 safety controller that interlocks critical conditions:

• No motion until limit switches confirm bleachers are either fully deployed or fully stored.
• Motion stops immediately if any sensor or hardwired e-stop is triggered.
• Proportional speed control limits acceleration/deceleration to prevent dynamic loads on hinges and deck interconnects.

The control panel sits on the front rail of the bottom deck or on a mounted pedestal. An operator can jog the system (inching mode) for fine positioning, or press "Deploy" or "Retract" for automatic motion to end-of-travel.

Mobility and Storage

Four industrial-duty swivel casters in the Roller Carriage allow the entire 3-ton assembly to be moved on gym floors. Two rear casters have Brake Solenoid electromagnetic brakes that lock when the system is deployed, preventing accidental rolling during events. When stored, the bleachers compress to a 0.8 m footprint, narrow enough to tuck into a standard gymnasium corner or alcove.

Handrail and Safety Protection

The Handrail Assembly includes perimeter safety rails around all sides, grab handles at stair spacing, and a Safety Bumper foam buffer running along the fold line. This bumper prevents fingers or clothing from being pinched as decks open and close.

Installation and Certification

Installation requires a dedicated 208/240 VAC 20 A circuit with overload protection. Gymnasium floor must support 40 kPa distributed load. Before first use, the system must pass ASTM F24 inspection (load testing, hinge torque check, safety switch continuity). Annual maintenance includes lubrication of hinges and chain, inspection of caster wheels, and functional testing of all limit switches and e-stops.