Selection,inStallation andUSage of HatcHeS
Tech NoTe

Hatches for utility structures are manufactured
from cast iron, aluminum and steel. The casting
requirements, in regard to concrete cover and required
steel reinforcing, differ depending on material type.
These requirements also vary based on expected load
and required hatch size. Using the right accessories,
casting the hatches and using the hatches according
to manufacturer’s recommendations, or specifications
such as ASTM C1802, will protect the structures
lifespan.

Fabricated HatcHes
Products utilizing steel or aluminum are typicallyreferred to as fabricated doors. These doors
transfer the applied load through beams to bearing
plates on each end. Unlike cast iron, these bearing
plates are not designed to adequately support thedesign loads. This area may require additional
reinforcement and concrete support to transfer
the design load.

Typical Traffic Bearing Hatch
Cast into Corner of Top Slab

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The use of an attached, fabricated skirt is strongly
recommended to ensure the bearing plate is supported by theprecast concrete structure. All fabricated hatches intended forloads heavier than pedestrian traffic should use a fabricatedskirt. If using an aluminum product, a bituminous coating shallbe applied to the areas of the skirt and frame in contact withconcrete. The alkalis in concrete are corrosive to aluminum
and will deteriorate an aluminum door over time.

Shear reinforcement, if necessary under the bearing surface, and properly consolidated concrete is required
under bearing end plates. Structural cracks in the concrete at these end supports will reduce the potential for thespecified door to meet the design loads.
Professional guidance and design is recommended for all structures using hatches. Engineered and stamped
designs shall be required for all traffic rated and airport designs. The required design varies with the clear openingof the hatch size, structure size and intended loading. This results in varying top slab thicknesses as well as
required reinforcing. Place any required drains on the side of the hatch, away from the ends of the load bearing
beams. If possible, it is efficient to place the load bearing beams directly over the wall of the structure.
Order the fabricated hatch with skirt
corresponding to the required slab thickness.
Provide a production drawing that locates the hatch
according to the clear opening or outside of theattached skirt. Ensure adequate concrete coveragearound the reinforcing by placing the reinforcing
clear of the frame and other components. It is also
important to have the hatch doors securely bolted
to the frame when closed. Otherwise, the applied
load will create impact and vibration in the frame,
damaging the precast concrete top slab and hatch.
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Successful production of precast utility structures is based on understanding the product specified, identifying thekey components, ordering the required accessories and casting them into the structure properly. Then, use thehatches according to manufacturer recommendations.

caSt iron HatcHes
Cast iron hatches are available in both“flange down”, which is set on top of aconcrete slab, and “flange up”, which iscast flush with the top of the slab.
Cast Iron hatches designed with a flangeup, or top flange, frame are intended to be“wet set” in concrete. The top flange
design generally eliminates the need forany additional anchoring typically used with“flange down” applications.

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Cast Iron hatches are available for a variety of loading requirements, ranging from light duty for pedestrian
traffic, to extra heavy duty for airfields and ports. Selecting a proper casting requires the services of a qualified
professional who knows how and where the hatch will be used, and has the training and experience necessary
to take into consideration all the circumstances of the intended application. That includes determining therequired strength, capacity and function as well as assessing the casting’s suitability for the location in which it
will be installed.
Gray iron and ductile iron are commonly used in cast iron hatches. Both are available in a variety of classes orgrades to suit the application. The frame of most hatches is cast in gray iron while the cover can be gray iron or
ductile iron. Typical specifications for gray iron would be Class 30B, Class 35B and Class 40A. Ductile iron is alsoavailable in several grades, with Grade 65-45-12 being the most common in the industry.
This publication is designed to provide accurate and authoritative information, however the National Precast Concrete Association does not guarantee the validity or accuracy of any data,
claim or opinion appearing in this publication. If engineering, legal or other professional services are required, the services of a competent professional should be obtained. The National
Precast Concrete Association does not assume and hereby disclaims liability to any person for any loss or damage caused by errors or omissions in this publication, regardless ofwhether such errors result from negligence, accident or any other cause whatsoever.

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