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242 ANDERSON ON THE DESIGN OF BOMB PROOF SHELTERS.

EXTRA MEETING.20 June, 1939.

SYDNEY BRYAN DONKIN, Past-President, in the Chair.The Chairman said that the Lecture that evening was entitled The

Design of Bomb-Proof Shelters and it would be given by Dr. DavidAnderson, a Member of Council of The Institution and Chairman of theDesign Panel, Engineering Precautions Air Raids) Committee. Itshould be emphasized that hesubject-matter of the Lecture had noconnexion whatever with the policy of shelters or the puttingdown of thevarious kinds of such shelters, but only with the design of them. Thepresent Lecture formed the thirdof a series arranged by The Institution.

Dr. Anderson was well known to all the members of The Institution,but others might be reminded of what he bad done and was doing. Hewas consulting engineer of renown and experience, having been connectedwith the Mersey tunnel, the Dartford tunnel, and the new tunnels for theLondon Passenger Transport Board. He had, also, specialized knowledgeof such work as was involved in shelter design.

Tbe Design Panel, of which he was Chairman, of the EngineeringPrecautions Air Raids) Committee had been formed by The Institution,with the addition of representativesnominated by heInstitutions ofMechanical, Electrical, andStructural Engineers, andbyhe RoyalInstitute of British Architects. It was formed a t the special request ofthe Home Office to study the information contained in the new A.R.P.Handbook No. 5, which had been issued during the past week, and theinformation which Dr. Anderson would give in his Lecture that eveningwould mainly be thesubject-matter of a new handbook which wouldshortly be issuedl.

The Design of Bomb-Proof Shelters.By DAVIDANDERSON, L.D., B.Sc., M. Inst. C E

Abridged Report e .Dr. Anderson said that the Committee had considered the matter in

considerable detail and had prepared altogether about thirty provisionaldesigns, including the three which had been completed for inclusion in5A copies of which can be obtained from H.M. Stationery Office.-Src. INST.C EThe full Report has been published by the Home Office as Structural HandbookCopies of the Lecture may be obtained on application to the Secretary.

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ANDERSON ON THE DESIQN OF BOMB-PROOF SHELTERS. 243theirReport. Attack by bombs might take various forms and beofvarying intensity, but inorder to be definite in theirrecommendations theCommittee had laid down four types of protection, namely :-Type Protect,ion.Type 2 Protection.Type 3 Protection.

Type 4 Protection.

Rased on resistance to blast and splinters, debrisloads and small incendiary bombs.Bascd on resistance to the direct hits of mediumweight indendiary bombs and high-explosive bombs.Designed to give protectionagainst the effects ofheavy high-explosive bombs. The standard adoptedwas considered to be adequate against the effects ofa medium-case bomb of the order of 500 lb. weightstriking a t its maximum velocity. It was alsoconsidered to be proof against light-case bombs ofconsiderably greater weight.Similar to Type 3 Protection, but designed to giveprotection against the effects of a heavy-case bomb.

Type 1 had already been standardized. Types 3 and 4 were consideredto be the most urgently required, and the Report dealt almost entirelywith those two, Type being reserved for later consideration.

The designs were based upon the shelters being divided into compart-mentswith not more than 100 persons in each compartment ; wheremore than 1 200 persons had to be protected i t was recommended that theshelters should be spaced at least 25 feet apart or some special arrangementsmade.

The shelters designed consisted essentially of two-storey structures ofa box form, either rectangular or circular, formed of reinforced concreteand placed generally half above and half below ground, easy access to thebasement storey being obtained by means of staircases. Shelters placedat a considerable depth below ground were not considered in detail,alt,hough it was realized that there should not be any great difficulty indesigning them to provide degrees of protection similar to those affordedby the recommended designs.

The action of a 500-lb. bomb on a concrete shelter had been studied indetail, and, to meet the combined effect of direct impact, disruptive forceof explosion and spalling effect on the inner surface, the thickness o theconcrete decided upon was 5 feet for the roof; 3 feet 3 inches for wallsabove ground, and 6 feet 6 inches below ground and 6 feet 6 inches for thebase, except in large shelters where under certain conditions the thicknesscould be progressively reduced to 2 feet 6 inches. For type 4 protectionthe thickness of the roof was increased to 7 feet 6 inches to give greaterprotection. Alternative methods of protecting the base by carrying downthe side walls to form a curtain,or by providing slabs on the ground to forman apron, were considered, but were found to be too costly in most cases.

The class of concrete to be adopted, the nature of the steel reinforce-

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244 ANDERSON ON THE DESIGN OF BOMB PROOF SHELTERSment, the internal lining to resist spalling, and anumber of practicaldetails were all nvestigated, and appropriate standards recommended.Particular study was made of the width of entrance required, etc. In thecase of the shelter to accommodate 1 200persons, the entrances had beenarranged so that the shelters could be occupied within 12 minute.

The Committee took steps to compare their recommendations withthe regulations adopted in othercountries, and found them tobe in generalagreement. Estimates were prepared of the cost per person for the variousprovisional designs, and those costs were found to range from 21 7 to 6per person. The costs of the designs that accompany the Report werefound to be :-about X25 9s. Od per person for the rectangular shelter for200 persons ; about 221 8s Od per person for the circular one, and aboutE17 10s. Od per person for the large shelter for 1 200 people.

A vote of thanks o he Lecturer was proposed by Sir CLEMENTHINDLEYresident-Elect, who stated that when one looked back on thesomewhat difficult history of air-raid shelters, he thought it wouldbeagreed t,hat a great sense of relief should be felt that, the ork of designingshelters was a t last in theands of competent people, and that the overn-ment and the administrators, who so often thought that they could doeverything without technical assistance, had gradually come to the viewth at the work was work for engineers, and had put it in the hands ofengineers. They were fortunate in having Dr. Anderson and his colleagueson the Panel available for translating the valuable information in Hand-book No. 5 into a form in which i t was of practical use to theengineer.

Mr. F. M. G . Du-Plat-Taylor seconded the vote of thanks, which waspassed hy acclamation.