This glossary is drawn from the "Glossary of Terms,"
pp. 223-236, in Waddell, J. A. L.,The Designing
of Ordinary Iron Highway Bridges. New York, J.
- A (top)
- Adjustable Member
- A member of a bridge the length
of which can be increased or diminished at will.
- Angle Iron
- Iron rolled into the shape shown in
section on Plate II., Fig. 3.
- The intersection of a brace with a chord or
flange; called also a panel point.
- Axis of Symmetry
- A line dividing an area into two
parts equal and similar to each other, and similarly disposed
to the line.
- B (top)
- A piece of iron flat or square in section.
- Slope, or inclination, to the vertical;
usually measured by the tangent of the angle, or so many inches
to the foot.
- Batter Brace
- The inclined end post of a bridge.
- A member intended to resist bending.
- Beam Hanger
- A rod or square bar supporting a floor
beam from a chord pin. (Plate I. and Plate II., Fig. 13.)
- Beam-hanger Nuts
- Nuts on the ends of beam hangers,
serving to press the floor beam against the feet of the posts
or against, the chord heads. (Plate IL, Fig. 13.)
- Beam-hanger Plate
- A plate placed beneath the end
of a floor beam for the beam-hanger nuts to rest against (Plate
II.,. Fig. I3.)
- Beam-trussing Posts
- Posts for trussing beams (P1ate
II., Fig. 16.)
- Beam-trussing Rods
- Diagonal rods for trussing beams.
(Plate II., Fig. 16.)
- A resting-place, usually for a pin or rivet
- The pressure on a bearing.
- Bed Plate
- A plate to distribute pressure upon masonry.
- The moment of a force or forces
which bend or tend to bend a piece.
- The stress produced in a piece by
- A frame of timber or iron, usually the former,
as a bent of false-work.
- Bent Eye
- An eye on the end of a bar, the plane
of which makes an angle with the direction of the 1ength of the
- The slope on the end of a piece.
- Bill of Material
- A list of various portions of
material giving dimensions and weights, or other quantitative
- A system of one or more pulleys or sheaves,
so arranged in a frame or shell as to multiply the power of the
rope passing around them, or to change its direction.
- Board Measure
- The measure of timber, the unit being
a piece one foot square and one inch thick.. Timber is sold at
so much per thousand feet board measure, usually written, per
M. b. m.
- An iron rod with a square head at one end,
and a thread and nut at the other: the head may sometimes be wanting.
- Generally a strut, but sometimes the term
is applied to a tie.
- A knee or knee brace to connect a post
or batter brace to an overhead strut. (Plate I.'or Plate II.,
- A beam made up of plates and angles
riveted together. (Plate IL, Fig. 13.)
- A rough edge or ridge left by a tool in cutting
metal. The term is sometimes used for a nut.
- Button Sett
- A tool for forming the heads of rivets.
- C (top)
- The upward curvature of a truss. It is measured
by the height of the middle point of the centre line of the lower
chord above the line joining the centres of end pins.
- Camber Blocks
- Blocks of wood used in erection,
so placed as to be easily renioved (Plate VII.)
- Cape Chisel
- A tool for cutting iron. It consists
of a rounded edge on the end of a short rod. The edge is very
obtuse, so as not to break easily.
- Centre of Gravity
- That point of a body about which
the weights of all the different portions balance.
- Channel, or Channel Bar
- Iron rolled into the shape
shown in section on Plate II., Fig. 1.
- Check Nut, or Lock Nut
- A contrivance to prevent
a nut from turning when subjected to shock.
- The upper or lower part of a truss, usually
horizontal, resisting compression or tension. (Plate I.)
- Chord Bar
- A member of the chord which is subjected
to tension. (Plate I.)
- Chord Head
- The enlarged end of a chord bar, through
which the pin passes.
- Chord Packing
- The arrangement of the bottom chord
of a truss.
- Clear Headway
- The vertical distance from the upper
surface of the floor to the lowest part of the overhead bracing.
It is a measure of the height of the highest vehicle that could
pass through the bridge.
- Clear Roadway
- The horizontal distance, measured
perpendicular1y to the planes of the trusses, between the inner
edges of the batter braces. It is a measure of the width of the
widest vehicle that could pass through the bridge.
- A narrow strip of wood nailed to something
for the purpose of keeping a piece of work in its proper place.
- Co-efficient of Friction
- A numerical quantity,
which, multiplied into the normal pressure, gives the frictional
resistance. It is equal to the natural tangent of the angle of
- Cold Chisel
- A tool for cutting iron.
- A pillar or strut; a long member which resists
- One of the parts into which a stress
may be resolved or divided.
- A stress which tends to shorten the
member which is subjected to it.
- Concentrated Load
- A load which is, or may be considered,
collected at one or more points.
- Continuous Spans
- Consecutive spans connected over
the points of support.
- Connecting Chord Heads
- Chord heads used to connect
bottom chord channels to pins. (Plate II, Fig. 10.)
- A plate used for connecting two
- An adjustable diagona1 which is not subjected
to stress by a uniformly distributed load covering the bridge.
- Countersunk Rivets
- Rivets, the heads of which are
let into one or both of the plates which they connect, so as to
leave a flush surface or surfaces.
- Two equal and parallel forces not acting
in the same line.
- Cover Plate
- A plate used to cover a joint, or to
connect two pieces of the top chord plate. (Plate II., Figs. 11
- A slow-motion machine, worked by a crank for
the purpose of winding a rope upon a drum, thereby raising a heavy
- D (top)
- To notch timber on to its bearing.
- Dead Load
- The weight of all the parts of the bridge itself,
and any thing that may remain upon it for any 1ength of time.
- Deck Bridge
- A bridge in which the passing loads come
upon the upper chords or the upper ends of the posts.
- Motion laterally, or at right ang1e
to the length of the piece. It is also used for the amount of
motion, and is generally expressed in inches.
- Depth of Truss
- The vertical distance between the
centre lines of upper and lower chords.
- A member running obliquely across a panel. In
this work all the diagonals except the batter braces are tension
- Diagram of Stresses
- A skeleton drawing of a truss, upon
which are written the stresses in the different members. (Plate
- Double Intersection
- The style of truss where the diagonals
cross the posts at the middle of their length, as in the bridge
shown on Plate I.
- Double-riveted Lacing
- Lacing in which each bar
is connected by two rivets at each end. (Plate II., Fig. 13.)
- Drift Bolt
- A round or square piece of iron, usually
from one to three feet long, without head or nut, used to connect
- Drift Pin
- A slightly tapering rod of hard steel,
used for niaking rivet holes coincide. Its use is more convenient
- E (top)
- Effective Area
- The gross area of a section, less
that lost by rivet or pin holes; the net area.
- Elastic Limit
- That intensity of stress at which the
ratio of stress over strains commences to show a decided change.
For wrought-iron it is from twelve to fifteen tons.
- A bill of material for a bridge,
so arranged as to facilitate the finding and placing of members
- Expansion Joint
- The connection of pedestal to bed-plate,
shown on Plate III.
- Expansion Rollers
- A set of half a dozen or more
turned rods of exactly the same diameter, placed under the shoe
plate at one end of a truss to permit of expansion and contraction.
(Plate II., Fig. 9.)
- Extension Plate
- A plate riveted to the end of a strut
channel, and projecting beyond it, to permit of the passage of
a pin. (Plate 11., Fig. 12.)
- A hole in the end of a member to permit of
the passage of a pin.
- Eye Bar
- A bar with an eye at each or one end.
- F (top)
- Factor, or Factor of Safety
- The ratio of ultimate load
to greatest allowable working-load. This term is getting out of
favor among engineers, as its use has been somewhat abused. There
is no such thing as a factor of safety for a well-proportioned
bridge, for each member should have an intensity of working-stress
proportionate to the character and amount of work which it has
- Fall Line
- A rope used in erection for raising and lowering
- Temporary timber work to support a bridge
- Felly Plank
- A guard rail so placed as to catch the felly
of a wheel, and thus prevent the vehicle from striking the truss.
(Plate II., Fig. I3.) In wide bridges a felly plank is often placed
midway between the trusses, to prevent vehicles passing from one
side of the bridge to the other.
- Field Riveting
- Riveting done in the field, or during
erection. It is the poorest and most expensive kind of riveting.
- Fixed End
- An end of a strut so firmly connected as to
prevent all motion of the strut in the neighborhood of the end.
- A plate the function of which is to make
flush two surfaces (Plate II., Fig. 12.)
- A small ring of iron or piece of pipe placed
on a pin in order to keep in place the members coupled thereon.
- Fixed Load
- A load remaining permanently, or for a considerable
length of time, upon a structure or portion of a structure.
- The upper or lower chord of a beam. It is the
principal part for resisting either compression or tension.
- Floor, or Flooring
- That part of the bridge which directly
receives the travel. (Plate IL, Fig. 13.)
- Floor Beam
- A beam to support a portion of the floor
and its load. (Plate I. and Plate II., Fig. 13.)
- An apparatus for heating iron.
- The carpenter work on timber.
- G (top)
- Giasticutus Rods
- A term (perhaps unauthorized, but in
common use among bridge builders) to denote a small horizontal
rod connecting the middle points of two adjacent posts of the
same truss, for the professed purpose of fixing or holding the
posts at the middle in order that they may be figured for half-length.
The benefit derived therefrom is more imaginary than real.
- Any structure to cross a chasm or opening. The
term is generally applied to short structures for places where
it is not advisable to use trusses; for instance, a plate girder,
or a rolled girder.
- Guard Rail
- See felly plank.
- Guys, or Guy Lines
- Lines for bracing the top of a pole,
derrick, or any similar apparatus.
- See radius of gyration.
- H (top)
- Hammered Head
- A head formed on the end of a bar by haznmering.
- Hand Lines
- Small ropes used in erection.
- Hand Rail, or Hand Railing
- An iron or wooden frame placed
on or near the outside of a bridge in order to prevent persons
or animals from falling therefrom. (Plate IV., or Plate II., Fig.
- Hand-rail Cap
- The upper longitudinal timber or timbers
of a wooden hand-railing. (Plate IL, Fig. 13.)
- Hand-rail Post
- Post for supporting a hand railing. (Plate
II., Fig. i~; Plate IV.)
- See clear headway.
- Hinged End
- An end of a strut connected only by a pin.
- The place at which the top chord meets the batter
- Hip Joint
- The joint of the top chord and batter brace.
- Hip Vertical
- A rod hung from the pin at the hip for
the purpose of suspending the floor beam.
- Holding-on Bar
- A lever to hold against one end of a
rivet while the head at the other end is being formed with a button
- Hub Plank
- A plank to protect the iron-work of the truss
from being struck by the hubs of passing wheels. (Plate II., Fig.
- I (top)
- A piece of rolled iron of the section shown on
Plate II., Fig. 2.
- Initial Tension
- The tension caused in any adjustable
member by screwing up the adjusting apparatus.
- The intensity of a stress is the amount of
stress upon a square inch of section.
- Intermediate Strut
- An overhead strut in high bridges,
attached to the posts of opposite trusses, and lying between the
upper lateral strut and the floor. In deck bridges, if used at
all, it would lie between the upper and lower lateral struts.
- J (top)
- A connection on the end of a strut similar to that
shown on Plate IL, Fig. 13.
- A place where two abutting or lapping pieces are
- A timber beam that supports part of the door and
its load. (Plate I. and Plate IL, Fig. 13.)
- K (top)
- Knee, or Knee Brace
- See bracket.
- L (top)
- A system of bars, not intersecting each
other at the middle, used to connect the two channels of a strut
in order to make them act as one member. (Plate II., Fig. 12.)
- A bar belonging to a system of lacing.
- Lateral Rod
- A tension diagonal of a lateral system.
- Lateral Strut
- A compression member of a lateral system.
- Lateral System
- A system of tension and compression members
forming the web of a horizontal truss connecting the opposite
chords of a bridge. Its purposes are to transmit wind pressure
to the piers or abutments, and to prevent undue vibration from
- A system of bars crossing each other at the
middle of their lengths, used to connect the two channels of a
strut in order to make them act as one member. (Plate II., Fig.
- Lattice Bar
- A bar belonging to a system of latticing.
- One of the two portions of an angle iron separated
from each other by the bend.
- Lever Arm
- The perpendicular from the centre of moments
to the line of action of a force. The lever arm of a couple is
the perpendicular distance between the lines of action of the
two equal and parallel forces.
- Live Load
- The moving or passing load upon a stnicture.
- Linville Truss (also called "Double Quadrangular,"
"Whipple," and "Double System Pratt"
- A truss with vertical posts and diagonal ties spanning
two panels. It is the truss represented on Plate I.
- Lock Nut
- See check nut.
- Loop Eye
- An eye on the end of a rod or square bar, elongated
into the form of a ioop, as shown on Plate II., Fig. 16.
- Lower Falsework
- The falsework below the level of the
- M (top)
- Main Diagonal
- A tension member of a truss, sloping upward
towards the nearer end of the span. Main diagonals in iron bridges
are not adjustable.
- The product of a force by its lever arm.
- Moment of Inertia
- Represented by the equation, I
= Apt = Zr2dA, whereA is the area of the section considered,
p the radius of gyration, andr the distance of any point
from an assumed line lying either in the surface or outside of
it: in other words, the moment of inertia of a surface about any
axis is the product of the area by the square of the radius of
gyration; or it is the summation of the products of each differential
of the area by the square of its distance from the axis. If the
axis lie in the surface, the moment of inertia is called a surface
moment of inertia; while, if the axis be perpendicular to the
surface, the moment of inertia is called a polar moment of inertia.
- Monkey Wrench
- A wrench capable of being adjusted so
as to fit nuts of different sizes.
- Moving Load
- See live load.
- A timber, usually from 6" by 6" to
12" by 12", at the bottom of a bent. It is laid horizontally
in a trench, and the posts of the bent rest upon it.
- N (top)
- Name Plate
- A plate of iron placed in a conspicuous position
on a bridge, containing the name of the maker or designer of the
- Negative Rotation
- Rotation in a direction opposite to
that of the hands of a watch.
- Net Section
- See effective area.
- Neutral Surface
- That part of a member subjected to bending,
which is neither extended nor compressed. In symmetrical wrought-iron
beams, with equal or nearly equal flanges, it is taken to be at
the centre line of the web.
- A small piece of iron with a threaded core to fit
on the screw end of a bolt, rod, or bar. (Plate II., Fig. 6.)
- O (top)
- Order Dill
- A form of bill used in ordering material
from the mannfacturers.
- Ornamental Work
- Fancy work at the portals of a bridge
to give it architectural effect (Plates I. and VI.)
- Overhead Bracing
- The upper lateral or sway bracing in
through bridges. The term is usually applied to the sway bracing,
if there be any; if not; to the upper lateral bracing.
- P (top)
- See chord packing;
- That portion of a truss between adjacent posts
or struts in Pratt truss bridges; called also a bay.
- Panel Length
- The distance between two adjacent panel
points of the same chord.
- Panel Point
- See apex.
- The foot of a batter brace or end post. (Plate
II., Fig. 9.)
- Permanent Set
- The alteration in length of a piece of
material which has been subjected to stress, remaining after the
stress has been removed.
- See column.
- Pilot Nut, or Pin Pilot
- A nut, one end of which is a
truncated cone, used to protect the thread on the end of a pin
when the latter is being driven into place. (Plate II., Fig. 5.)
- A cylindrical piece of iron used to connect bridge
members. (Plate II., Fig. 5.)
- The distance between centres of consecutive
rivets of the same row.
- Plane of Symmetry
- A plane dividing a body into two equal
and symmetrical parts similarly disposed in reference to the plane.
- Tools and apparatus used in construction.
- A piece of fiat iron wider than a bar. The common
distinction between the two is that a plate is attached to something
else, and acts with it, while a bar is an independent member.
- Plate Girder
- A beam, built of plates and angles, used
to span a small opening, generally less than forty feet.
- Pony Truss
- A truss so shallow as not to permit the use
of overhead bracing.
- The space between the batter braces at one end
of a bridge. Sometimes the term is applied to the portal bracing,
- Portal Bracing
- The combination of struts and ties in
the plane of the batter braces at a portal, which transfers the
wind pressure from the upper lateral system to the abutment or
- Portal Strut
- A strut belonging to the portal bracing.
- Positive Rotation
- Rotation in the direction of the hands
of a watch.
- A vertical strut. (Plate I.)
- Pratt Truss (called also the "Murphy-Whipple,"
or "Quadrangular" truss)
- A single-intersection
truss with vertical struts and diagonal ties.
- Q (top)
- Quadrangudar Truss
- See Pratt truss.
- R (top)
- Radius of Gyration
- The radius of gyration of any surface
in reference to an axis is the distance from the axis to that
point of the surface in which, if the whole area were concentrated,
the moment of inertia in reference to the axis would be unchanged.
It is therefore equal to the square root of the ratio of the moment
of inertia over the area.
- To enlarge a rivet hole.
- A tool for enlarging rivet holes.
- Re-enforcing Plate
- A plate used for the purpose of providing
additional pin bearing, or strength, to compensate for material
cut away. (Plate II., Figs. 11 and 13.)
- To divide a force into component parts.
- A short piece of round iron ticrhtly connecting
two or more thicknesses of metal, and having, when in place, a
head at each end.
- The passage-way of a bridge for vehicles; usually
means clear roadway,q. v.
- A piece of round iron.
- Rolled Beam
- An I-beam. (Plate II., Fig. 2.)
- See expansion roller.
- Roller Frame
- A light frame of iron for holding the rollers
in position. (Plate II., Fig. 9.)
- Roller Plate
- The plate upon which the rollers rest,
and which itself rests upon the masonry.
- Rope Sling
- See sling.
- A line, or string; as, a run of joists.
- S (top)
- The extension or compression of a piece of material
- Shear, or Shearing-Stress
- The resistance which a body
offers to the passage, or to the tendency to passage, of, one
section along the next consecutive section.
- A list of portions of a bridge, arranged
in a manner to facilitate counting and checking when the material
is received after shipment.
- Another term for pedestal,q.v.
- Shoe Plate
- The plate on the under side of the shoe,
resting on the rollers, bed-plate, or masonry.
- Side Bracing
- A bracing for pony trusses to attach
the panels of the top chord to the floor beams prolonged, in order
to fix the panel points of the top chord. (Plate III.)
- Roadways at the sides of a bridge for
- Single Intersection
- That style of truss in which the
diagonals do not cross the posts. It is represented in skeleton
on Plate V.
- Skeleton Drawing
- A drawing which shows only the
centre lines of members, such as a diagram of stresses. (Plate
- Skew Bridge
- A bridge in which the horizontal lines
joining corresponding panel points of the opposite trusses are
oblique to the planes of the trusses.
- A heavy hammer, or mallet.
- Sleeve Nut
- An elongated nut, the core at one end
having a right-hand thread, and that at the other a left-hand
thread. Its office is to lengthen or shorten a tension member.
(Plate II., Fig. i6.)
- A loop of rope, very useful in erection for making
a hasty attachment.
- Inclination to a horizontal plane.
- Snatch Block
- A block with one side capable of being
opened for the insertion of the rope. Its office is to change
the direction of the rope.
- The length of a bridge from centre to centre
of end pins or bearings.
- Large nails for timber work. (Plate II.,
- To spread at one end the two main portions
of a member.
- A joint connected by means of plates.
- Splice Plate
- A connecting plate at a joint. (Plate
II., Fig. 12.)
- The distance apart laterally.
- Staggered Rivets
- Rivets are said to be staggered when
each rivet of one row is opposite to the middle of the space between
two rivets of the next row.
- Static Load
- Dead load,q.v.
- Stay Plate
- A plate always used at the end of a
system of lacing or latticing. (Plate II., Fig. 12.)
- An angle iron used to stiffen the web
of a beam. (Plate II., Fig. 13.)
- A piece of iron used to stiffen the web
of a beam: it may be of angle or tee section. (Plate IL, Fig.
- The extension or compression of a piece
of material which is or has been under stress.
- The internal resisting force of a piece
of material which is strained.
- A member which rasists compression.
- The punching of rivet holes which have
to be afterwards enlarged by reaming.
- Sway Bracing
- Bracing transverse to the planes of the
trusses. Its objects are to resist wind pressure, and to prevent
undue vibration from passing loads. (Plate I.)
- T (top)
- Table of Data
- A list of the known circumstances that
affect the designing of a structure.
- A screw for cutting a thread in a nut.
- Tee or T iron
- A piece of rolled iron of the section
shown on Plate II., Fig. 4.
- A stress tending to elongate a body.
- The spiral part of a screw or nut.
- Through Bridge
- A bridge with overhead bracing.
- A tension member; generally refers to a main
- Timber Truck
- A small, strong wooden frame, with an iron
roller set entirely below the upper surface. It is used in bridge
erection for moving large timbers and heavy weights along a runway.
- Part of a riveting outfit; used for holding and
carrying heated rivets.
- Transverse Component
- A component in a transverse direction;
generally intended for a component perpendicular to the planes
of the trusses.
- An assemblage of tension and compression members
so arranged as to transmit loads from intermediate points to the
- A poor substitute for lacing or latticing.
(Plate II., Fig. 8, Plate VI.)
- Turn Buckle
- Similar to a sleeve nut, and for the same
purpose. The sides are open, so that a crowbar may be inserted
for the purpose of screwing up. Turn buckles are used for larger
bars or rods than are sleeve nuts. (Plate IL, Fig. i6.)
- U (top)
- Ultimate Strength
- The greatest load that a portion of
material can bear.
- Uniform Load
- A load so distributed over an entire structure,
that equal lengths everywhere receive equal portions.
- A piece of iron, in the shape of the letter U,
through which passes the threaded end of a rod, and which affords
a bearing for the nut, with room to screw up the latter. Its use
is not permissible in first-class bridge construction.
- Upper Falsework
- The falsework that lies above the level
of the upper chords.
- Upset End
- An end of a rod or bar enlarged for the cutting
thereon of a screw-thread.
- V (top)
- Vibration Rod
- A tension member for vertical or portal
sway bracing. (Plate I.)
- W (top)
- A piece of cast or wrought iron to distribute
the pressure of a bolt-head or nut over timber. (Plate II., Fig.
- The portion of a truss or beam between the flanges.
Its office is principally to resist shear.
- Welded Heads
- Heads first worked into shape, then welded
on the bars.
- Whipple Truss
- See Linville truss.
- Wind Shakes
- Cracks in timber caused by the wind while
the free was living.
- Drawings containing all the measurements
necessary for construction.
- The stress, usually the greatest stress,
to which a piece of material is or should be subjected. Sometimes
incorrectly employed for intensity of working-stress.
- A tool for screwing up nuts.