3.3　Types and Conformation of Foundations

3.3.1　The types and conformation of metallurgical equipment foundations shall be defined as follows:

1　The types of foundations shall be designed as per the process and equipment requirements to allow for easy installation，operation and maintenance of equipment；

2　Foundations，in simple & regular shapes，shall be logically constructed，with definite loads applied，featuring adequate rigidity，to avoid or minimize abrupt change in rigidity；

3　The types of foundations shall be selected by taking into account the engineering geologic conditions，hydrogeologic conditions，environmental and construction conditions.

3.3.2　Depending on the different space demand by different plants，equipment types，process and equipment layout and production operations as well as the characteristics of loads to be applied，metallurgical equipment foundations shall be of masstype，walltype，piertype，frametype，rafttype，pittype，boxtype，or a combination of any two or more types above.

3.3.3　Equipment and units of the same process line as well as those which have direct influence upon their normal operation should siton the same monolithic foundation.If it's not possible to have them supported on the same monolithic foundation，differential settlement between foundations shall be within the limitsto allownormal operation of the equipment and units.

3.3.4　Equipment in the same continuous production line（including underground works such as the basements adjoining the equipment foundations）should sit on combined monolithic foundations like continuous boxtype，or raft type foundations.

3.3.5　For technical revamping projects，wholly or partially assembled monolithic foundations can be applied to the metallurgical equipment to reduce the construction period，provided that good experience in similar projects is available and the conditions permit.

3.3.6　The depth of foundations shall be determined as per the type of the equipment，embedded depth of anchor bolts，underground space demand by the process equipment，the depth of pipe trenches，floor level of the adjacent basements，the depth of the adjacent foundations and underground works，the types and conformation of foundations，the groundand environmental conditions as well as the magnitude and nature of loads applied to the foundations.The foundations should be shallow as long as adequate stability and foundation deformation can be guaranteed.The depth of high-rise equipment foundations shall meet the requirements of bearing capacity，deformation and stability.In case of rock subgrades，the foundations shall be deep enough to meet the anti-sliding requirements.The effects of frost heaving and thaw collapse shall be taken into account when determining the depth of foundations on seasonal frozensoils.

3.3.7　Pipeline trenches inside equipment foundations shall be routed logically to minimize crossing and overlapping.A single foundation shall have identical bottom level wherever possible.

3.3.8　The structural dimensions of foundations shall be as follows:

1　The foundation beds should be no thinner than 100mm，with width no 100mm smaller than the foundation.In case of waterproof concrete slabs in soft soils，the concrete beds shall be no thinner than 150mm.

2　The distance between the edge of equipment bases and the edge of the foundations should be no smaller than 100mm.

3　The layout dimensions and embedment depth of anchor bolts shall be as specified in Section 3.5 of this Code.

4　Separate maintenance accesses inside the foundations should have clear width no smaller than 800mm and clear height no smaller than 2，000mm.The pre-opened holes through which mechanical equipment will pass shall be sized by considering the requirements of maintenance personnel.

5　Ladders for maintenance purpose inside the foundations shall be sized as follows:Inclined ladders should be no narrower than 800mm，while steel ones should have a slope of 45° and concrete ones a slope of 30°.In case of straight ladders，the holes should be sized at 800mm×800mm，no narrower than 400mm.Safety cages should be provided for straight ladders higher than 3m.

6　Slabs of pipeline trenches should be no thinner than 200mm，and the trench walls should be no thinner than 150mm in case of one-sided reinforcement and 200mm in case of double-sided reinforcement.

7　Basements，raft type foundations，boxtype foundations and pit type foundations shall be sized as follows:

1）The thickness of slabs should be no smaller than 1/10 the depth of the foundations and no smaller than 1/8 the spacing of the columns.

2）The thickness of exterior walls should be no smaller than 1/10 the height of the walls，and the cross section of the walls may vary with the depth.

3）The thickness of interior walls should be 1/20-1/16 the height of the walls，and should be no smaller than 200mm.

4）Beam and slab type top slabs shouldbe no thinner than 200mm.

5）The spacings of columns should be 5m-8m.

6）The side length of cross section of the columns should be no smaller than 1/16 the height of the columns，and should be no smaller than 400mm.

3.3.9　Equipment foundations and the adjacent foundations shall be arranged as follows:

1　When a shallow and small equipment foundation is to sit close to a large equipment foundation，the former should be cantilevered from the latter（Fig.3.3.9-1）.If it's not applicable，bed concrete may be poured into the pit underneath the small foundation（Fig.3.3.9-2）.

2　If an equipment foundation on soil is to sit close to a building column foundation but their bottoms are not at the same level（Fig.3.3.9-3），the two foundations shall be adequately spaced，depending on the nature of the ground and loads.The clear distance between the foundations（S）may be assumed as 1-2 times the bottom elevation difference between the two foundations.If the above requirements cannot be met，the bed underneath the shallow foundation may be thickened up to the bottomlevel of the deep foundation.In case the bottom level difference between the two foundations is considerably huge，reliable pit supports shall be provided during construction，and the loads of the shallow foundation upon the deep foundation shall be considered.

3　If an equipment foundation is anticipated to have some interference witha building column foundation，combined raft type foundation may be preferred.If a foundation has to be isolated，the affected part of the equipment foundation may be removed and partially cantilevered.The horizontal gap between the equipment foundation and the building column foundation should be no smaller than 30mm，and the vertical gap shall meet the requirements for differential foundation settlements（Fig.3.3.9-4）.

4　If a building column foundation is to extend through a waterproof boxtype equipment foundation or basement，it must be isolatedand enclosing sleeves may be provided around the column foundation.The horizontal gap between the sleeves and the building column foundation should be no smaller than 50mm（Fig.3.3.9-5）.

3.3.10　The layout of and fire protection for metallurgical equipment foundations，basements，cable tunnels and pipe corridorsshall be designed in accordance with the current national standard Code of Design for Fire Protection and Prevention of Iron and Steel Metallurgy Enterprises（GB 50414）.

3.3.11　For waterproof pit type，box type metallurgical equipment foundations and underground works such as basements，cable tunnels and pipe corridors which must be waterproof and their bottom elevation is lower than the designed ground water level，waterproof works，construction and water seepage control shall follow the current national standard Codes for Water Protection and Prevention of Underground Works（GB 50108）.However，the waterproof zoning and water protection and prevention design of equipment foundations and underground works shall be made as follows:

1　Waterproof concrete works shall be employed，and reliable water protection and prevention shall be made to construction joints，expansion joints and pipe joints.In case of strict waterprotection and prevention requirements，waterproof exterior paints or external waterproof coils shall be applied，depending on the specific conditions.Metallic waterproof layersmay be applied to special equipment foundations which have very strict waterprotection and prevention requirements.

2　When waterproof concrete worksareto be used，auxiliary facilities such as internal drainage ditches and sump pits shall be provided.

3　For underground works in a mountainous region where strict waterprotection and preventionis required，external seepage water drainage or blind ditch systems may be provided additionally if the ground water is perched water and can be drained by gravity.

4　Waterproof zoning and waterprotection and prevention design of metallurgical equipment foundations and underground works shall be madeas per Appendix C to this Code.

5　The impermeability gradesof waterproof concrete shall be determined as per Section 3.4.1 of this Code.

3.3.12　Expansion joints shall be provided as follows:

1　Expansion joints shall be provided in line with the equipment and equipment layout，not interfering with normal operation of the equipment and production line.

2　The maximum spacings of expansion joints shall be as per Table 3.3.12.

3　Monolithic foundations shall be employed for equipment complete with direct drivesor rigid connections，so no expansion joints shall be provided.Raft type foundations and continuous boxtype foundations may not be provided with expansion joints in order to meet the requirements of process，equipment layout and normal production.

4　For ultralong and ultrawide foundations in which expansion joints are not to be provided，post pouring bands shall be employed for pouring by segments.Alternate pouring method may be adopted and reliable measures shall be taken properly if good experience in similar projects is available（Fig.3.3.12）.The post pouring bands may be spaced in the same way as for the expansion joints.Segments specific for alternate pouring method should be 20m-30m long preferrably，40m long at maximum.The slabs may be divided into longer segments，but no longer than 50m each.

5　If double-column expansion joints are provided for elevated equipment foundations or platform frames，the double-column foundations may be monolithic，without any deformation joints.

6　Whena underground tunnel or pipe corridor is to be extended from the exterior wall of an equipment foundation，equipment line foundation and continuous box type foundation or basement，expansion joints or post pouring bands should be provided for the tunnel and pipe corridor at least 300mm away from the outer surface of the foundation.For expansion joints，the adverse effects caused by differential settlements between the foundation and the tunnel or corridor shall be taken into account，and proper countermeasures shall be taken.

7　Expansion joints should be 20mm-30mm wide.Waterstops shall be embedded for the expansion joints of waterproof underground works.If water seepage is likely in top slabs，the expansion joints of the top slab shall also be provided with waterstops to form a closed loop together with the waterstops for outer walls and slabs.Rubber waterstops may be used if the ambient temperature is equal to atmospheric temperature，and metallic waterstops may be used when the ambient temperature is above 50℃.The expansion joints for which waterstops are embedded shall have a minimum structural thickness of 300mm.

3.3.13　Effective means such as flexible connections and protective conduits shall be taken for pipelines extending out of the foundations or basements to protect them from damage due to unequal settlements.If water protection and prevention is required，the connections shall be designed in accordance with the current national standard Code for Water Protection and Prevention of Underground Works（GB 50108）.

3.3.14　Safety railings shall be installed around the pits，uncoverederection openings and platforms.In accordance with the current national standard Safety Requirements for Fixed Industrial Railings（GB 4053.3），the safety railings shall be at least 1，050mm tall，and provided with skirt boards at least 100mm tall.The railings should be made of steel tubes no smaller than 48mm in diameter.The railings shall be at least 1，200mm tall when the ground clearing is equal to or bigger than 20m.

3.3.15　Protections shall be properly provided for equipment foundations which are directly exposed to slag splashing，heating，impingement by equipment and materials，or erosion by acids，alkalis or oil.Foundations and floors which may be in direct contact with the leaked molten steel，hot metal or molten slag shall be provided with protective layers，and measures shall be taken properly to prevent waterlogging.

3.3.16　As for a large equipment foundation sitting on a perfectly or fairly complete rocky subgrade，the hindering constraint effects of the bedrock upon the foundation contraction shall be considered.When necessary，isolation layers should be provided between the foundation bottom and the bedrock within an appropriate reach of the foundation，and anti-hindering layers shall be arranged on the foundation steps deformed due to hindering and on the side hindered due to the abrupt change in flat surface（Fig.3.3.16-1，2）.

3.3.17　When an equipment foundation is to sit on non-rocky subgrade and limited settlements and inclination are required by process and equipment，settlement measuring points shall be provided and the measuring requirements shall be specified.Settlement measuring points shall be provided properly and measurements shall be done as perAppendix E to this Code.

3.3.18　Reinforcement of metallurgical equipment foundations shall meet the relevant requirements in respective Chapters of this Code.To those not covered in the Chapters，the following rules shall apply:

1　For structural members of the metallurgical equipment foundations，the designed reinforcement ratio of the longitudinally stressed rebars shall be no smaller than the minimum reinforcement ratio as prescribed in the current national standard Code for Design of Concrete Structures（GB 50010）.Only in the following cases can the minimum reinforcement ratio be reduced appropriately:

1）The minimum reinforcement ratio of tensile rebars horizontally placed in the ground slabs may be 0.15%.

2）For flexural slabs and large eccentrically-compressed piers which feature very thick section due to arrangement or anti-floating requirements，the minimum reinforcement ratio of tensile rebars may vary with the ratio of applied actual internal forces to the bearing capacity of the section.

2　When reinforcement is necessary to the construction，the reinforcement ratio of horizontal rebars and that of rebarson the top and bottom of the slabs in massive equipment foundations and in equipment foundation walls shall be no smaller than the limits specified in Tables 3.3.18-1，3.3.18-2 below.Massive concrete should be reinforced with rebars of smaller diameters and smaller spacings，provided that the quantity of reinforcement is the same.

3　When the longitudinal rebars of the same row are too densely arranged in the member section，it is allowed to arrange every two rebars（twin bars）or to separatethe rebars into more rows，depending on the specific circumstances and the positions of reinforcement.The anchorage length of the twin bars shall be defined according to the diameter of a single rebar which has equal section area as the twin bars.

4　The thickness of concrete covers for rebars shall be determined according to the environment category，structure type and concrete strength in acordance with the current national standard Code for Design of Concrete Structures（GB 50010）.Specifically，the concrete covers for longitudinally stressed rebars at the bottom of the foundations and slabs，on the outer side of short foundation columns and underground works walls in direct contact with soil shall be no thinner than 40mm.If there is no bed，the concrete covers for rebars at the bottom of the foundations or slabs shall be no thinner than 70mm.This may not be applicable to pit type，boxtype equipment foundations，the top of the basement slabs，the inner side of exterior walls not in contact with the soils.However，they shall meet the requirements for the minimum thickness of concrete covers for slabs and walls，etc.

5　When aconcrete cover is thicker than 100mm because the stressed rebars at the top of slabs for equipment foundation or basement are arranged in full length underneath the drainage ditches and shear groove of equipment baseplate，it shall be provided with reinforcing mesh with rebars of 4mm-8mm in diameter and spacing 100mm-200mm.

6　Side horizontal rebars in ultralong pit type，box type equipment foundation walls without expansion joints may be arranged outside the vertical rebars.

7　Structural strengthening rebars shall be arranged in the following members and parts as follows:

1）Structural strengthening rebars shall be arranged for holes in slabs and walls if the holes have side length or diameters greater than 300mm，or if the holes have side length or diameters equal to or smaller than 300mm but the rebars have to be cut off as they cannot bypass the holes.The section size of the structural strengthening rebars shall be no smaller than 50% that of the cut rebars on each side.When a the hole has side length or diameter greater than 10，000mm，beams should be provided aside if it's in a slab，and concealed beams and concealed columns should be installed aside if it's in a wall.

2）Horizontal constructional rebars shall be arranged vertically over the full length of the entire walls or pit walls on the top within the thickness range.The diameters of the rebars should be no smaller than that of the horizontal rebars in the walls or pit walls and the spacings should be no greater than 150mm.

3）For monolithic poured connections between walls or pit walls and the large-section building column foundations or massive equipment foundations，small-diameter additional rebars should be arranged between the horizontal rebars to reduce the spacings of the rebars.The reinforcement ratio of the horizontal additional rebars should be no smaller than 15% that of the horizontal rebars in the walls or pit walls，and the rebars embedded in the walls or pit walls should be no shorter than 1，500mm，while the rebars anchored in the short foundation columns or massive equipment foundations should be long enough to allow adequate anchorage and should be no shorter than 300mm.

4）If an equipment foundation is subject to impact loads or significant loads existing underneath the equipment base，reinforcing mesh with rebars of 12mm in diameter and spacing 100mm shall be provided on the top of the foundation or other necessary positions.The reinforcing mesh may be installed in two layers，with layer spacing of 100mm.

5）For removable bolts and anchor slab bolts subject to heavy tension，two layers of reinforcing mesh with rebars of 12mm in diameter，spacing of 100mm should be provided above the anchor slabs，with layer spacing of 100mm.The reinforcing mesh shall extend beyond the anchor slabs for a sufficient distance to allow adequate anchorage.

6）If the distance between the anchor bolt/pre-opened bolt holes and the equipment foundation edge does not meet the requirements in Section 3.5.4 of this Code，strengthening shear-resisting rebars shall be arranged accordingly where necessary.

7）When asecondary grouting layer is as thick as 100mm or more，reinforcing mesh should be provided，with rebars of 6mm or greater in diameter，spacing no more than 100mm.

8）Strengthening rebars should be arranged for shear grooves of equipment slabs on the top of the equipment foundation.The strengthening rebars may be arranged around the rectangular or polygonal openings formed by the outline of the shear grooves.

8　If the reinforcement for any equipment foundation is not covered in this Section，the current national standards Code for Design of Concrete Structures（GB 50010）and Code for Design of Building Foundation（GB 50007）shall apply.