CONTENTS
| CHAPTER I. | |
| INTRODUCTION—GIRDER BEARINGS. | |
| PAGE | |
| Pressure distribution—Square and skew bearings—Fixed bearings—Knuckles—Rollers—Yield of supports | [1] |
| CHAPTER II. | |
| MAIN GIRDERS. | |
| Plate webs: Improper loading of flanges—Twisting of girders—Remedial measures—Cracks in webs—Stiffening of webs—T stiffeners | [9] |
| Open webs: Common faults—Top booms—Buckling of bottom booms—Counterbracing—Flat members | [17] |
| CHAPTER III. | |
| BRIDGE FLOORS. | |
| Liability to defects—Impact—Ends of cross and longitudinal girders—Awkward riveting—Fixed ends to cross girders—Plated floor—Liberal depths desirable—Type connections—Effect of “skew” on floor—Water-tightness—Drainage—Timber floors—Jack arches—Corrugated sheeting—Ballast—Rail joints—Effect of main girders on floors | [20] |
| CHAPTER IV. | |
| BRACING. | |
| Effect of bracing on girders—Influence of skew on bracing—Flat bars—Overhead girders—Main girders stiffened from floor—Stiffening of light girders—Incomplete bracing—Tall piers—Sea piers | [34] |
| CHAPTER V. | |
| RIVETED CONNECTIONS. | |
| Latitude in practice—Laboratory experiments—Care in considering practical instances—Main girder web rivets—Lattice girders investigated—Rivets in small girders—Faulty bridge floor—Stresses in rivets—Cross girder connections—Tension in rivets—Defective rivets—Loose rivets—Table of actual rivet stresses—Bearing pressure—Permissible stresses—Proposed table—Immunity of road bridges from loose rivets—Rivet spacing | [45] |
| CHAPTER VI. | |
| HIGH STRESS. | |
| Elastic limit—Care in calculation—Impact—Examples of high stress—Early examples of high stress in steel girders—Tabulated examples—General remarks | [61] |
| CHAPTER VII. | |
| DEFORMATIONS. | |
| Various kinds—Flexing of girder flanges—Examples—Settlement deformations—Creeping—Temperature changes—Local distortions—Imperfect workmanship—Deformation of cast-iron arches | [73] |
| CHAPTER VIII. | |
| DEFLECTIONS. | |
| Differences as between new work and old—Influence of booms and web structure on deflection—Yield of rivets and stiffness of connections—Working formulæ—Set—Effect of floor system—Deflection diagrams—Loads quickly applied—“Drop” loads—Flexible girders—Measuring deflections—New method of observing deflections—Effect of running load | [85] |
| CHAPTER IX. | |
| DECAY AND PAINTING. | |
| Examples of rusting of wrought-iron girders—Girder over sea-water—Rate of rusting—Steelwork—Precautions—Red-lead—Repainting—Scraping—Girders built into masonry—Cast iron—Effect of sea-water on cast iron—Examples—Tabulated observations—Percentage of submersion—Quality of metal | [96] |
| CHAPTER X. | |
| EXAMINATION, REPAIR, AND STRENGTHENING OF RIVETED BRIDGES. | |
| Purpose—Methods of examination—Calculations—Stress in old work—Methods of reducing stress—Repair—Loose rivets—Replacing wasted flange plates—Adding new to old sections—Principles governing additions—Example—Strengthening lattice girder bracings—Bracing between girders—Strengthening floors—Distributing girders | [107] |
| CHAPTER XI. | |
| STRENGTHENING OF RIVETED BRIDGES BY CENTRE GIRDERS. | |
| Principal methods in use—Method of calculation—Adjustments—Connections—Method of execution—Checks—Effect of skew on method considered—Results of calculation for a typical case—Probable error—Practical examples—Special case—Method of determining flexure curves | [122] |
| CHAPTER XII. | |
| CAST-IRON BRIDGES. | |
| Limitations of cast iron—Stress examples—Advantages and disadvantages—Foundry stresses—Examples—Want of ductility of cast iron—Repairs—Restricted possibilities | [141] |
| CHAPTER XIII. | |
| TIMBER BRIDGES. | |
| Perishable nature—Causes of decay—Sag—Lateral bracing—Piles—Uncertainty respecting decay—Examples—Conditions and practice favourable to durability—Bracing—Protection—Repair—Piles—Cost | [149] |
| CHAPTER XIV. | |
| MASONRY BRIDGES. | |
| Definition—Cause of defects or failure—Spreading of abutments—Closing in—Example—Stop piers—Example of failure—Strength of rubble arch—Equilibrium of arches—Effect of vibration on masonry—Safety centring—Methods of repair—Pointing—Rough dressed stonework | [157] |
| CHAPTER XV. | |
| LIFE OF BRIDGES—RELATIVE MERITS. | |
| Previous history—Causes of limited life—Tabulated examples of short-lived metallic bridges—Timber and masonry bridges—Durability—Maintenance charges—First cost—Comparative merits—Choice of material | [165] |
| CHAPTER XVI. | |
| RECONSTRUCTION AND WIDENING OF BRIDGES. | |
| CONCLUSION. | |
| Measuring up—Railway under-bridges—Methods of reconstruction in common use—Reconstruction of bridges of many openings—Timber staging—Traffic arrangements—Sunday work—Railway over-bridges—Widenings—Junction of new and old work—Concluding remarks—Study of old bridgework | [172] |
| INDEX | [187] |
THE
ANATOMY OF BRIDGEWORK.
CHAPTER I.
INTRODUCTION.
No book has, so far as the author is aware, been written upon that aspect of bridgework to be treated in the following pages. No excuse need, therefore, be given for adding to the already large amount of published matter dealing with bridges. Indeed, as it too often happens that the designing of such constructions, and their after-maintenance, are in this country entirely separated, it cannot but be useful to give such results of the behaviour of bridges, whether new or old, as have come under observation.
In the early days of metallic bridges there was of necessity no experience available to guide the engineer in his endeavour to avoid objectionable features in design, and he was, as a result, compelled to rely upon his own foresight and judgment in any attempt to anticipate the effects of those influences to which his work might later be subject. How heavily handicapped he must have been under these conditions is evident from the mass of information since acquired by the experimental study of the behaviour of metals under stress, and the growth of the literature of bridgework during the last forty years. That many mistakes were made is little occasion for surprise; rather is it a cause for admiration that some very fine bridges, still in use, were the product of that time. Much may be learned from the study of defects and failures, even though they be of such a character that no experienced designer would now furnish like examples.