FOUNDATION WORK By A. G. MOULTON The term foundation work is generally considered to cover the construction of all supporting masonry including embedded steel up to that level known as grade. It may comprise curb and area walls, retaining walls, isolated column footings, foundation girders, wall footings, elevator pits, machine foundations, etc. The difficulties attending upon foundation work will be found to increase almost directly proportionate with its depth. In present day practice, concrete is almost universally used for foundations. On smaller buildings such use may be restricted to footings only, with the retaining or foundation walls themselves run up in brick or hollow tile, but on larger work, where greater strength is required to resist earth pressure, concrete, either plain or reinforced, will be the probable choice. The general excavation or grading having been completed and footing trenches and piers opened up, concreting of same should immediately follow. If the soil will stand unsupported, forms are not necessarily required for a footing course, and the excavation should be made to neat lines. 25. Pumping of Excavations.-On all foundation work, pumping equipment of some kind should be provided so that trenches and pits can be pumped out before concreting is undertaken. The size and scope of the undertaking will determine the capacity and number of pumps required. These may be anything from the small hand operated diaphragm pump up to the larger capacity centrifugal and triplex types electrically or steam driven. The diaphragm pump, mounted on skids or trucks and gasoline driven, will find its use on any foundation job. For the deeper pits, the steam syphon or the pulsometer type of pump will probably give the best results. A liberal boiler capacity should be provided, however, if they are chosen. If the lift to the sewer or surface is so great as to require pressure pumps, it will be found desirable to first gather the ground water in a sump pit or temporary basin by means of diaphragm pumps, so that the sand and grit may settle out before being lifted. It should be remembered that in open basements, particularly in clay where the surface water does not readily soak away, a 3-in. rain fall may tie up the entire operation for 48 hr. or longer. Under such conditions, a pumping plant of adequate capacity is always a good investment. 26. Damage to Excavations by Rainfall and Surface Water.-Proper protection should be afforded against damage from surface water flowing into the excavation from neighboring streets. At the height of a heavy rain storm, with the sewers taxed to their capacity, this may become a serious menace to the work, particularly if the street banks are sheet piled and the surface water finds entrance behind the sheeting. A small earth or sand dam thrown up on the street beforehand, parallel to the work, may prevent this damage. Precaution should be taken to see that old sewer stubs entering the site are solidly blocked up to resist a back flow, and that all street sewers and water mains that have been exposed are substantially shored or braced. 27. Concreting Plant.-In choosing the proper type of concreting plant for any particular job, so many factors must enter into consideration that nothing but the most general suggestions would be of value here. Ordinarily, that type which is the most conservative on hand labor should be the adopted one. Mechanical concrete mixers are now obtainable in so many sizes and types that one will be found to meet any given condition of foundation work. As a result, hand mixed concrete is now seldom to be considered. For street and curb walls, the small two and one bag mixers that can be readily moved from place to place and the charge spouted direct into the forms, will probably be found the most economical unit. For column footings, where the individual yardage is not sufficient to warrant the progressive movement of the mixer, the 2- or 4-yd. mixers and concrete buggies will provide the solution. For caisson work, where the yardage in each pier is considerable, a permanently established mixer serving through 1-yd. tilting cars on a narrow gage track, will give good satisfaction. Upon being dumped, the cars deliver their load into a portable receiving hopper suspended at the top of the well, and from there to the bottom through a flexible telescopic spout. This spout, approximately 10 in. in diameter, of light iron, is made up in sectional lengths of about 4 ft. each, the sections being removed from the bottom as the concrete rises in the well, The use of a tower with gravity chutes for light foundation work will not as a general rule work out economically. If on the other hand, however, the character of the superstructure indicates the gravity system as being proper, its early installation and use on the foundations would be permissible. Generally speaking, when in doubt as to the capacity of the mixer required, select the smaller size. This leaves you in a position where with a steady run-off before you, you can speed up the number of batches to readily obtain the desired output, whereas with an interrupted flow, the idle forces back of the mixer will be at a minimum. With the larger mixer under such conditions all lost or idle time is correspondingly felt on the payroll. Availability of storage space and convenience of delivery for the dry materials are important determining factors in the selection and location of the plant. It should be remembered that the opportunities are infinitely greater for wasting labor back of a mixer than in front of it. 28. Forms and Reinforcement for Foundations.-Form work and the placing of reinforcement for foundation work does not, as a rule, present the problems that are present in superstructure work. Piers and footing courses require only the simplest knowledge of form building, and the wall forms are the only ones that may call for a show in skillful design. The general subject of forms, their design and construction, is considered in Art. 39. 29. Waterproofing of Foundations and Basements.Waterproofing of basements is so intimately connected with foundation work that it is well to consider it at this point. Various methods of waterproofing are in use, any one of which may be encountered by the builder. There is the integral compound, either powder or liquid in form, which is introduced in the concrete at the time of mixing, and directions for the use of which are furnished by the manufacturer. Another method is the coating of the finished wall with special preparations, such as ironite or the hydrolithic compounds. These are usually applied to the interior face of the wall, permitting the work to be done at any convenient time. A third method is the coating of the exterior of the wall with coal tar pitch, in which is embedded two or more plies of roofing felt. When conditions require a so-called pressure basement, a connecting strip of felt and tar is carried through all exterior walls as well as over all column footings at a level a few inches below the finished basement floor. After the walls are finished, the coating on the back of the walls is applied and connected to a lap provided on these horizontal strips and eventually it is also connected up to a sheet which extends under the entire basement floor. For basements which are under a constant head of water, this is one of the most successful methods, and if carried out with due care will provide ample and lasting protection. When it is impractical to provide sufficient space in which to apply the exterior coating on walls after they are in place, the felt and tar may be mopped on to a 4-in. brick or tile wall, which is run up in advance and against which the permanent wall is then installed. If this be of concrete construction, then the vertical felt course as well as all horizontal ones should be protected against damage by a safety course of cement mortar trowelled on. Pressure should be relieved until the last through some conveniently located sump pit at which time this place may be sealed; and if the waterproofing is skillfully applied the basement will be tight thereafter. STRUCTURAL STEEL WORK BY A. G. MOULTON Structural steel is utilized so frequently in the various phases of building construction that a general knowledge of its proper and economical handling is most essential. Aside from its use as sheet piling, and in superstructure work, steel is used to some extent in building operations as grillage beams and foundation girders which support the column bases or stools, which, in turn, carry the columns. In some designs the cast stools will be eliminated and rolled or cast steel billets substituted. 30. Setting Grillages.-Grillage is commonly used as two sets of steel beams on each footing-one placed on top of the other, but reversed as to direction of length. The individual beams making up a set of grillage are tied together by means of bolts and pipe supporters, and wherever the assembled unit is not beyond the capacity of the field forces to handle, it will be found desirable to have the assembling done at the mill. The concrete of footings or piers where it receives the grillage should be left by the mason 2 or 3 in. below the final level so as to enable the more accurate setting of screeds. Should there be a division of responsibility between 1 For a more complete treatment, see Hool and Johnson's "Concrete Engineers' Handbook," pp. 82 to 90. the mason and the steel erectors, the best results will be obtained by having the mason set the screeds. These should be brought to exact level by engineers' instruments and solidly grouted into place. Pieces of 11⁄2-in. angle back up, or wooden strips about 1 × 11⁄2 in., make satisfactory screeds. Grillage beams are adjusted for position laterally by means of lines stretched through, on column center points and projected down by the aid of small plumb bobs. If an engineer's transit is available, more exact work will be obtainable. An accurate set of grillage beams, which means the same for stools and columns, is well worth the effort to obtain. A tolerance of in., plus and minus, both in level and line is unsatisfactory practice. As soon as beams have been set and checked by the engineer, they should be concreted in to guard against accidental shifting. On the top set, hand-hold clearance should be left to insert column bolts, if same are required. 31. Equipment For Erecting Steel Frame Buildings.-On steel frame buildings, the erection equipment will be delivered and set up while the foundation work is being carried on. The selection as to type of derrick is governed by the size of the building site and the character of the work to be handled. If it is such as to give proper play to the revolving boom, then either a guy derrick, stiff leg, or the so-called Chicago boom, may be used. Where proper guying can be obtained and on lots 40 ft. or more in width, the guy derrick will prove the most economical. Where suitable anchorage is difficult to find, or where the guys themselves would be objectionable, as on narrow corner lots, the stiff leg derrick will probably be chosen. On narrow lots, with neighboring building on one or both sides, of height equal or greater than the new building, then the Chicago boom may be used. This presupposes that the consent of the adjoining owner for such use of his structure can be obtained. The expedient of setting the derrick on top of the adjoining building should be adopted only as a last resort. Greater initial cost, the discomfort of tenants through vibration and confusion of workmen going to and from the roof, the expense of keeping roof in water-tight condition during operation, and the permanent repairs later, will all go to more than offset any saving gained through not having to make additional moves in carrying the derrick up with the new work. 32. Locating Derricks for Erection.-Having chosen the type and number of derricks required, the exact location of mast centers should be duly determined. This should be such as will allow the greatest range of action over the building area, suitable consideration being given to the point from which loads of steel will be received, and sufficient length of boom reserved for that purpose. A 33. Cycle of Erecting Operations with Derricks. With the guy derrick, full revolution of the boom, or 360 deg., is possible; with the stiff leg but 270 deg. can be reached with full swing; and with the Chicago boom but 180 deg. The greater range of the guy derrick makes it much to be preferred. For building work, booms from 75 to 90 ft. in length are used. guy derrick with an 85-ft. boom will develop the greatest efficiency when serving an area of approximately 10,000 sq. ft. The tonnage involved in such area, will generally work out so as to provide a 4-day cycle between raises. When two or more derricks are engaged on the same operation, precision of raises must be observed otherwise, confusion will result in the shipping, hauling, and unloading of steel at the building site. The expense of an idle derrick with full crew waiting for steel is such that any departure from the estimated schedule is promptly disclosed through the daily cost statements. On a 4-day cycle, one day will be required in receiving the steel and elevating it to the working floor. Such columns as will not obstruct the play of the boom will be set between loads. The second day will be used in sorting out the various beams and girders and throwing them out on the working floor in the various panels to which they belong. When sorting steel, the boom should never swing without a load, and the active foreman will so arrange his work. Sorting hooks are used for handling individual beams and, as soon as a number of beams for the same panel have been found, a sling is thrown around them and they are delivered to the proper location. The third day, the erection of the two tiers above the working floor is made, and on the fourth day the derrick is closed in and raised to the new level, and planking laid for the next working floor. When working on shops, factory buildings, and other low structures where the tonnage is mainly in crane girders and roof trusses, one or more poles working abreast and moved back out of the way of the advancing work, will be the method chosen. On such class of work, if the tonnage is sufficient and direct, and railroad connection is convenient, the locomotive crane will be found more economical than the poles. On heavier and higher structures, such as train sheds, power houses, etc., which exceed the working range of either poles or locomotive cranes, resort is then had to the traveler, with one or two booms mounted on same, as conditions may require. 34. Choice of Power for Derricks. Wherever electric power is available, it is generally to be preferred over steam for the derrick hoists, particularly on high buildings, where to over come the excessive drum size required to hold the necessary length of cable otherwise required, the hoists are themselves raised to levels midway in the building. Greater cleanliness, the avoidance of the coal and ash problem, to say nothing of the time saved in not having to raise steam, are all in favor of the electric equipment. 35. Bolting and Plumbing of Superstructure.-As steel work is erected, it is loosely bolted by the connectors, except in those panels which carry the load of the derrick. These sections should be bolted up 100 %, and all tie-rods, if any, inserted and drawn to place before the derricks are raised. Before riveting is started, certain plumbing of columns may be required. Generally, this will be found in connection with the corners of the building and those columns adjacent to the elevator shafts. The great refinement which has entered into both shop detailing and fabrication of steel work during recent years, has made unnecessary, to a large extent, the plumbing heretofore required. Where plumbing is needed, it is accomplished by means of diagonal cables strung in a vertical plane and tightened by means of turn-buckles or steamboat ratchets. As soon as the work is riveted, the plumbing guys can be removed. 36. Riveting. With good average workmanship on the part of the fabricating shop, it is possible to start driving on the floor panels as soon as the beams have been raised to position and by keeping one or more riveting gangs engaged above the working floor, or that where the derrick sets, they will have the top tier driven before the deck planking is raised to become the new working floor. The riveters then drop back and catch the intermediate tier, returning again on the third day to the new upper level and the cycle is repeated. This method is extremely valuable as a time saver, inasmuch as it permits the centering for the floor system to keep directly behind the derricks. 37. Steelwork the Pacemaker.-Steelwork being one of the principal lines of work, should be made the pacemaker for the balance of the trades; therefore, it is doubly essential that a good, clean job, with all points caught up as it goes, should be given. With such an example, other trades are more apt to accept the invitation and follow along similar lines. On the other hand, if the job is not cleaned up as it goes, and the riveting or painting is allowed to drag, then the effect will be immediate, the following trades will be strung out to unnecessary limits, and the progress of the whole building will suffer delay. FLOOR CONSTRUCTION By A. G. MOULTON Uniformly progressive installation of the various floor systems in a building, whatever may be their type, is a healthful indication of the progress of the structure as a whole. The more even the rate at which floors are installed, and in steel frame buildings, the more closely their construction is kept up with that of the supporting steel or walls, the better will be that building's progress. This, perhaps, will be more readily understood when it is considered that on buildings of more than the one floor level each succeeding floor system as installed furnishes just that needed additional space on which to advance the trades in sequence, and provides an opening for the next and newest trade on the lower level. Ordinarily, the normal progress of trades up to the point of plastering is through the building from the bottom up. From that point on, in fireproof buildings of 8 stories and under, other conditions enter into consideration and it may be found advisable to start the finishing trades from the top and work downward. On buildings above 8 stories in height, where a normal schedule has been maintained, this change in direction can be made only at the expense of a definite delay in the final completion of the building. In view of the importance of the rate at which floors are constructed, it can be seen that every effort should be made to schedule the delivery of materials so that the floor installations may proceed uninterrupted at the predetermined pace. 38. Centering for Floors.—In all cases, some type of centering or forms will be required, the selection and design of which are usually left to the discretion of the builder. Having reached a decision as to the type, consideration is then given as to the quantity of centering which should be provided in order to give uninterrupted service. Reference to the building schedule indicates the allotted time from finish to finish of the respective floor systems, while the type of system and the season of year in which the construction is proceeding determines the length of time that should elapse between the placing and stripping of a set of forms or centers. With these two factors known, the extent of centering required will easily be determined. On steel frame buildings with short or semi-long span arch construction, the centering can be hung from above with considerable advantage, inasmuch as it leaves the story below unobstructed by shores or props. For the longspan arch the support from below provides the more feasible method. 39. Forms for Concrete.In the design of forms, centers, and other false work, careful consideration should be given to the probable methods of removal—that is, the design should be such that the forms can be taken down with a minimum of effort and with the least possible damage to the parts involved. This will be better realized when it is understood that over half the expense of concrete construction is made up in form costs plus the labor of removal. As a consequence, any labor economy of this nature that can be incorporated in the design will be found to multiply itself throughout the building, since the forms, through easy handling, are capable of being re-used. If satisfactory results are to be obtained, careful attention should be given to the kind and type of lumber to be employed, to the arrangement of joints at internal angles where one section abuts another, to the adjustment of supports and props so as to permit of early and partial stripping, to the application of form oil or other coating to the inside of forms before using, to the cure of that ever prevalent abuse of unnecessary nailing, and to the limited use of camber in girder and beam forms. On buildings of multiple stories, where forms are used on an average of three or four times, it can be safely assumed that, if the above precautions are taken to make possible such re-use, then all the initial requirements as to stability and tightness will likewise have been covered. The knowledge and experience of the builder will generally enable him to select proper sizes of lumber and supports without resort to special calculations. If in doubt, however, reference can be had to the many tables which have been prepared on the subject, and which are available for all conditions usually to be met with. Methods by which the concrete will be transferred to the forms should be considered, and sufficient bracing be provided to compensate for undue loads from that source. Horizontal members should be able to support the weight of concrete and the construction load. Vertical members must resist a hydrostatic pressure of about 145 lb. for each vertical foot of height. On all types of concrete arches between steel beams, it is highly desirable to keep the runway plank and workmen off the centers or panels as much as possible. The location of runway plank should be determined in advance, and proper supports provided that will not interfere with reinforcement and other items entering into the construction. On all operations of importance-and it is hard to conceive any items of structural concrete which would not classify as such-a careful and well organized system of inspection should be provided that shall remain in force from the time the forms are started until their final removal from the building. Such service is a necessary part of the contractor's organization, even though supplemented by the owner or designing engineer. Individual inspectors should be carefully instructed as to their respective duties, and a comprehensive system of daily reports installed to insure their adherence thereto. The quality of dry materials, the method of storage, the handling and proportioning of the materials, the erection and thorough cleaning of forms before filling, the operation of pouring, the watching against possible settlements or distortions of forms during that period, the care of concrete surfaces while undergoing the setting process, as well as the proper length of time to intervene before stripping, are all matters of too vital importance to impose upon the unsupported judgment of the construction foreman. He, as a rule, is too engrossed with the question of speed and initial cost to make possible an appraisal of such items at their true value. 39a. Lumber Forms.-Spruce and pine, either Norway or Southern, are the lumbers most generally used for form work, partially seasoned wood being the best. Hemlock is not desirable for forms owing to its inability to weather while standing exposed. For all surfaces where the concrete is to be later exposed, dressed lumber should be used. For flat surfaces, such as wall or floor panels, shiplap is preferable, although tongue-and-groove is satisfactory, and even square edge may be used if precaution is taken to provide sufficient supporting members to prevent buckling of the individual boards. For columns and girder bottoms, 1 For a complete treatment of "Forms" including their design, see Hool and Johnson's "Concrete Engineers' Handbook," pp. 93 to 137. |