sacrificial anode - the anode in a cathodic protection system 

sacrificial coating -  a coating over the base material to provide protection to the base material; examples include galvanizing on steel and aluclading on aluminum 

sacrificial protection - see CATHODIC PROTECTION 

sacrificial thickness - additional material thickness provided for extra service life of a member in an aggressive environment 

saddle - a member located upon the topmost portion of the tower of a suspension bridge which acts as a bearing surface for the catenary cable passing over it 

safe load - the load which a structure can safely support

safety belt - a harness or belt worn in conjunction with a safety line to prevent falling a long distance when working at heights 

safety curb - a curb between 9 inches and 24 inches wide serving as a limited use refuge or walkway for pedestrians crossing a bridge 

safety factor - see FACTOR OF SAFETY 

sag - to sink or bend downward due to weight or pressure 

scab - a plank bolted over the joint between two timber members to hold them in correct alignment and strengthen the joint; a short piece of I-beam or other structural shape attached to the flange or web of a metal pile to increase its resistance to penetration; also known as scab piece 

scaling - the gradual deterioration of a concrete surface due to the failure of the cement paste caused by chemical attack or freeze/thaw cycles

scour - erosion of a river bed area caused by stream flow 

scour protection - protection of submerged material by steel sheet piling, rip rap, a mattress, or combination of such methods  

scuba - a portable breathing device for free swimming divers; self-contained underwater breathing apparatus 

scupper - an  opening in the floor portion of a bridge to provide means for rain or other water accumulated upon the roadway surface to drain through it into the space beneath the structure 

seam weld - a weld joining the edges of two members placed in contact; in general, it is not a stress carrying weld 

seat - a base on which an object or member is placed 

seat angle - a piece of angle attached upon the side of a member to provide support for a connecting member either temporarily during its erection or permanently; also known as a shelf angle 

secondary member - a  member that is carried by other members and does not resist traffic loads 

section loss -  loss of a members cross sectional area usually by corrosion or decay 

seepage -  the slow movement of water through a material 

segmental - constructed of individual pieces or segments which are collectively joined to form the whole 

segmental arch - a circular arch in which the intrados is less than a semi-circle 

segregation - the state of being separated 

semi-stub abutment - cantilever abutment founded part way up the slope, intermediate in size between a shoulder abutment and a stub abutment 

shear - the load acting across a beam near its support 

shear stress - the shear force per unit of cross-sectional area; also referred to as diagonal tensile stress 

sheet pile cofferdam - a wall-like barrier composed of driven piling constructed to surround the area to be occupied by a structure and permit dewatering of the enclosure so that the excavation  may be produced in the open air 

sheet piles - flattened Z-shaped interlocking  piles driven into the ground to keep earth or water out of an excavation or to protect an embankment 

sheet piling - a general or collective term used to describe a number of sheet piles installed to form a crib, cofferdam, bulkhead, etc.; also known as sheeting

shelf angle -  see SEAT ANGLE 

shim - a thin plate inserted between two elements to fix their relative position and to transmit bearing stress 

shoe - a pedestal-shaped member beneath the superstructure bearing that transmits and distributes loads to the substructure bearing area 

shop - a factory or workshop 

shore - a strut or prop placed against or beneath a structure to restrain movement 

shoulder abutment - a cantilever abutment extending from the grade line of the road below to that of the road overhead. Usually set just off the shoulder 

shoulder area - see ROADWAY SHOULDER AREA 

sidewalk - the portion of the bridge floor area serving pedestrian traffic only  

sidewalk bracket - frame attached to and projecting from the outside of a girder to serve as a support for the sidewalk stringers, floor and railing or parapet 

silt - very finely divided siliceous or other hard rock material removed from its mother rock through erosive action rather than chemical decomposition 

simple span - the span of a bridge or element which begins at one support and ends at an adjacent support 

S-I-P forms - see STAY-IN-PLACE FORMS, FORMS 

skew angle - the angle produced when the longitudinal members of a bridge are not perpendicular to the substructure; the skew angle is the acute angle between the alignment of the bridge and a line perpendicular to the centerline of the substructure units 

skewback - the inclined support at each end of a segmental arch 

skewback shoe - the member transmitting the thrust of an arch to the skewback course or cushion course of an abutment or piers; also known as skewback pedestal 

slab - a flat beam, usually of reinforced concrete, which supports load by flexure 

slab bridge - a bridge having a superstructure composed of a reinforced concrete slab constructed either as a single unit or as a series of narrow slabs placed parallel with the roadway alignment and spanning the space between the supporting abutments  

slide - a sliding down of the soil on a slope because of an increase in load or a removal of support at the foot; also known as landslide 

slope - the inclination of a surface expressed as one unit of rise or fall for so many horizontal units

slope protection - a thin surfacing of stone, concrete or other material deposited upon a sloped surface to prevent its disintegration by rain, wind or other erosive action; also known as slope pavement 

slot weld - see PLUG WELD 

soffit - see INTRADOS 

soldier beam - a steel pile driven into the earth with its projecting butt end used as a cantilever beam 

soldier pile wall - a series of soldier beams supporting horizontal lagging to retain an excavated surface; commonly used in limited right-of-way applications 

sole plate - a plate attached to the bottom flange of a beam that distributes the reaction of the bearing to the beam 

sounding - determining the depth of water by an echo-sounder or sounding line 

spall - circular or oval depression in concrete caused by a separation of a portion of the surface concrete, revealing a fracture parallel with or slightly inclined to the surface 

span - the distance between the supports of a beam; the distance between the faces of the substructure elements; the complete superstructure of a single span bridge or a corresponding integral unit of a multiple span structure; see CLEAR SPAN 

spandrel - the space bounded by the arch extrados and the horizontal member above it 

spandrel column - a column constructed on the rib of an arch span and serving as a support for the deck construction of an open spandrel arch; see OPEN SPANDREL ARCH 

spandrel fill - the fill material placed within the spandrel space of a closed spandrel arch 

spandrel tie - a wall or a beam-like member connecting the spandrel walls of an arch and securing them against bulging and other deformation; in stone masonry arches the spandrel tie walls served to some extent as counterforts 

spandrel wall - a wall built on the extrados of an arch filling the space below the deck; see TIE WALLS 

specifications - a detailed description of requirements, materials, dimensions, etc. for a bridge which cannot be shown on the drawings; also known as specs 

spider - inspection access equipment consisting of a bucket or basket which is supported by a vertical wire rope cable; the cable spool is located under the floor of the bucket; the system is powered by compressed air 

splice - a structural joint between members to extend their effective length 

spread footing - a footing which is wide and usually made of reinforced concrete; ideally suited for foundation material with moderate bearing capacity 

springing line - the horizontal line within the face surface of an abutment or pier at which the intrados of an arch takes its beginning or origin 

spur dike - a projecting jetty-like construction placed adjacent to an abutment to prevent stream scour and undermining of the abutment foundation and to reduce the accumulation of stream debris against to the upstream side of the abutment 

stage - inspection access equipment consisting of a flat platform supported by horizontal wire-rope cables; the stage is then slid along the cables to the desired position; a stage is typically 20 inches wide, with a variety of lengths available 

statics - the study of forces and bodies at rest 

stationing - a system of measuring distance along a  baseline 

stay-in-place forms - a prefabricated metal concrete deck form that will remain in place after the concrete has set; see FORMS 

stay plate - a tie plate or diagonal brace to prevent movement 

steel - an alloy of iron, carbon, and various other elements and metals 

stem - the vertical wall portion of an abutment retaining wall, or solid pier; see BREASTWALL 

stiffener - a small member attached to another member to transfer stress and to prevent buckling 

stiffening girder - a girder incorporated in a suspension bridge to distribute the traffic loads uniformly among the suspenders and reduce local deflections 

stiffening truss - a truss incorporated in a suspension bridge to distribute the traffic loads uniformly among the suspenders and reduce local deflections 

stirrup - U-shaped bar providing a stirrup-like support for a member in timber and metal bridges; U-shaped bar placed in concrete constructions to resist diagonal tension (shear) stresses 

stone masonry - the portion of a structure composed of stone 

straight abutment - an abutment whose stem and wings are in the same plane or whose stem is included within a length of retaining wall 

strain - the change in length of a body produced by the application of external forces, measured in units of length; this is the proportional relation of the amount of change in length divided by the original length 

strand - a number of wires grouped together by twisting

stress - the force acting across a unit area in a solid material 

stress concentration - those concentrations of stress caused by a sudden change of cross section in a member 

stress cycle  - the variation in stress at a point with the passage of live load; from initial dead load value to the maximum additional live load value and back  

stress raiser -  a detail which causes stress concentration 

stress reversal  - change of stress type from tension (+) to compression (-) or vice versa 

stress sheet - a drawing showing  all computed stresses resulting from the application of a system of loads together with the design composition of the individual members resulting from the application of assumed unit stresses for the material to be used in the structure 

stringer - a longitudinal beam supporting the bridge deck 

structural analysis - an analysis of a structure (bridge) to determine the interaction of members and their consequent stresses 

structural member - an individual piece, like a beam or strut, which is an integral part of a structure 

structural redundancy -  that part of redundancy where the extra elements of support exist due to continuity in the framing element 

structural shapes - the various types of rolled iron and steel having flat, round, angle, channel, "I", "H", "Z" and other cross-sectional shapes adapted to the construction of the metal members incorporated in reinforced foundations, substructures and superstructures 

structural stability -  the ability of a structure to maintain its normal configuration, not collapse or tip in any way, under existing and expected loads 

structural tee - a tee-shaped rolled member formed by cutting a wide flange longitudinally along the centerline of web 

structure - something, such as a bridge, that is built and designed to sustain a load 

strut - a piece or member acting to resist compressive stress

stub abutment - an abutment within the topmost portion of the end of an embankment or slope and, therefore, having a relatively small vertical height; while often engaging and supported upon piles driven through the underlying embankment or in-situ material, stubs may also be founded on gravel fill, the embankment, or natural ground itself 

sub-panel - a truss panel divided into two parts by an intermediate web member, generally by a subdiagonal or a hanger