This drill hall is 170 x 250 feet outside and about 86 feet in extreme height above the tops of the piers.
The framework is entirely of steel with seven main roof trusses 26 feet apart, and two 45-degree hip trusses [see Fig. 230]. These trusses and the four secondary hip trusses are all seated on brick piers with concrete footings which, for the main trusses, are 12 feet square and 3 feet thick. Each of the main piers has four 21-inch bolts 10 feet long attached to large steel plates bedded in the concrete, and has a granite capstone 5 feet square and 18 inches thick.
The main roof trusses are riveted three-hinged arch ribs of 163 1/2 feet span and 73 feet 5 5/8 inches rise, center to center of pins, the general shape of the trusses being as shown in Fig. 232. The lower chord of the roof truss is approximately a parabolic line having its axis horizontal and about 3 feet below the centers of the end pins. The top chord is vertical to the roof line and thence is straight for a short distance and curves with a long radius to near the apex. This outline was designed with great care to avoid the tendency of the top chord to approach the bottom chord and form a neck below the apex. Each chord is made of two web plates, two angles and one or more cover plates. Each web member is made of two or four angles, latticed. All rivet holes were reamed, and where connections were bolted, finished bolts were used. The hinge pins are all of hard steel, 7 inches in diameter, and are locked in place to the ribs and pedestals by pairs of jaw plates with full holes on each member. The end pins of each main truss are connected together by a pair of horizontal round bars 2\ inches in diameter with upset ends and sleeve-nut connections. These bars are supported at frequent intervals by iron stands on brick piers, and they are connected to the end pins by short sections of 5 1/4 x 1 1/4-inch eye-bars. The hip trusses are similar to the semi-trusses of the main arch ribs, but have no bottom horizontal ties.
*From the Engineering Record of May 26, 1900.
Fig. 230. - Half Plan of Roof, Newark Drill Hall.
Fig. 231. - Half Elevation of Drill Hall Framing.
Fig. 232. - Diagram of Main Trusses.
The main roof trusses are connected by twelve lines of purlin trusses and six lines of lantern purlins, including the double apex line which is covered by a ridge roll connecting the opposite halves of the lantern frames. There is a system of diagonal lateral rods in all panels of main trusses and purlins, in the planes of the top chords, and there are longitudinal lattice girders and diagonal angles in the vertical panels between the ends of the main trusses. Both ends of the main trusses are fixed to the pedestals and their anchor bolts are proportioned for the shear from wind strains. Temperature movements of the trusses are assumed to be compensated by the rise and fall of the crown. Wooden rafters, parallel to the top chords are carried on the purlins and receive the sheathing boards which are covered with slate. Photographs of the trusses and additional details are published in the Engineering Record.