Joined: 26 Jan 2003
|Posted: Tue Nov 04, 2003 4:20 pm Post subject: Second set of Answers to Qestions
The second set of answers by Prof Kalyanraman, to the questions raised from October 19 to October 29, 2003, have been posted on Article #8, on the "Articles" page on the SEFI website (www.sefindia.org).
The answers are also appended at the bottom of this email, but for better readibility, please download from the Articles page
ANSWERS TO THE QUESTIONS RAISED DURING E-CONFERENCE
Question: Part of Cl. 184.108.40.206 perhaps should read (suggested change in quotes):
Where the cross section of the member varies within the length Lm, the "minimum" value
of ry and the maximum value of xt should be used.
Since ry is in numerator and xt in denominator. Also, it might be a good idea to explain
the basis of the magic formula given in this clause, may be in a commentary. Formulae corresponding to values given in various tables or graphs will help software developers.
I agree to the point of Mr. Rudra, those tables, charts in code should be accompanied
with the related formulas. This is not only useful for programming; it will also give clear picture of properties/relationship of various parameters of the structure. It will also help in designing the members (by hearting formulae) even if charts are not available.
Ans: For all the tables and charts presented in the IS: 800 draft equations have been presented to the extent they are available. Explanations of the equations in the codes will be presented in the commentary.
Question: I went to Himachal Pradesh when last incident of cloud burst was take place. We don't have any provisions of such disasters in any of our IS codes and over there I saw a whole bridge was taken away by flash flood so I just want to say that can we make any arrangements in codes for particularly in this type of areas so we can save more lives .I think the factor of safety in this type of region should be more as compare to other areas. -Mihir Joshi
Ans: Such flooding due to cloud burst and the corresponding bridge pier scouring/ washout are a part of hydraulic studies while planning a bridge. The corresponding force on piers is a part of bridge sub-structure code. These are outside the scope of IS: 800.
Question: Not much has been mentioned about local buckling which is an important factor for using hollow sections esp when one of the walls of the columns connected to a beam or a tension of compression member. It may be critical for free lips of H sections when under compression. Such criteria exists for cold-formed sections for thicknesses upto 8 mm (BS 5950). Can the same be extended further for sections of higher thicknesses-Vijay Patil
I agree with Vijay. In fact I would suggest that RHS and CHS should be covered in a different code altogether. - Rudra Nevatia
Ans: Adherence to the b/t limits given in Table 3.1 will ensure that buckling will not take place in hot rolled /fabricated sections
Question: So far I have not come across any guideline in the draft code for flexural members braced along tension flange. This is a very common occurrence in continuous construction - Rudra Nevatia
Ans: Such information is to be obtained from specialist literature. However using the code provisions one can conservatively design such bottom compression flange, conservatively, by assuming the beam upto point of inflection as a cantilever.
Question:There seems to be a discrepancy between Cl. 220.127.116.11 and Cl. 9.2.2. Perhaps Cl. 18.104.22.168 should just point to Cl. 9.2.2. . - Rudra Nevatia
Ans: We do not see any discrepancy. The limiting shear above which the moment capacity should be decreased.
Question: I was particularly looking for 1 clause contained in the current IS800, which limits the web. Flange thickness of primary member to 4mm and secondary member to 2mm. I could not find it in the draft. Is it proposed to do away with this requirement?
- Sundar Chandramouli
Ans: The minimum thickness requirement from durability point of view has not been included in the draft code since the durability requirement in section 15 of the draft code would ensure adequate protection for all thicknesses.
Question: There was a query on 10% stiffness at base of column. This requirement was introduced in British Code. A paper was published on the subject in Structural Engineer in '80s. If I remember correctly, the idea was to provide for *some* moment for design of components downwards of column base. Perhaps a better solution would be to assume the column as pinned at base and design base plate, pedestal and footing for 10% of the moment capacity of column.- - Rudra Nevatia
Ans: Section 4.3.4 provision on pedestal and foundation modeling could ensure this and is similar to BS 5950 clause 22.214.171.124.
Question: I was looking for slenderness coefficients for columns supporting trusses but I could not get it. The previous code (APPENDIX - H) if i am right, had a very clear pictorial presentation for slenderness coefficient for industrial structures; this seems to be missing in this code. Appendix - E, which deals with this, seems to be silent on what I am looking for. If there are any other references to column - truss combination
Ans: Appendix E in draft IS: 800 is similar to Appendix C in old code and contains all the recommendation for industrial building column. As far as the boundary conditions to be used in these columns the designer needs to understand the boundary condition in actual design. Unless the top of the column is laterally restrained against translation by bracing system sway restraint cannot be assumed.
Question: In continuation with the view points of Mr. Jignesh Shah I would like to point out that neither in the earlier IS: 800 nor in the newly drafted IS: 800 has any provision of relative displacement of the top of rail while the crane is in operation. In industry buildings with high crane capacity relative displacement of the top of rail becomes a critical aspect from serviceability point of view. A definite recommendation in this regard in given by the Russian Code of practice is reproduced below with heavy service conditions. Refer Clause No. 10.7 & Table46 of Snip II - B.3-72
1> H/2500 (with plane structural scheme)
2> H/4000 (with 3D structural scheme)
where, H = Height of column from u/s of column to the top of crane rail It has been observed the above clauses make the frame very heavy and thereby uneconomic. So the plant owners for smooth serviceability of crane and to reduce vibration have restricted the relative displacement to 10mm to 15mm. So I would request the Committee members of IS: 800 to introduce a clause, which will be a guideline for the relative displacement of the top of the rail -Alokes Guha
Ans: We will introduce a restriction on the relative displacement between rails of a crane as suggested. We would like to obtain some suggestion for this, as well as details of similar restriction available in other codes.
Question: What are the measures to be taken in case of composite construction where there may be different cases of only columns are composite and the beams are not or vice versa .Coming to Design of composite structures it is not mentioned at all except in the appendix that to for vibration of floors. But in India composite steel deck floor are still not used because the codes are not available. Neither the clients nor the manufacturers want to spend on experimental design. In India the steel structure can be economical if it is used as a composite structure. One of the INSDAG's publications for design of composite floors (deck span) clearly says that the design example is based on BS 5950 as no mention of it is found in IS: 800 now that the code is being revised it is necessary to incorporate composite section designs. - Vijay Patil
Ans: There is a special code IS: 11384 for the design of composite structures.
Question: I want the fig points to be considered: -
1. I worked in a cement plant. Whatever the air pollution control equipments are installed, there is dust near junction points of conveyors etc., packing plant too. Hence whenever design of trusses are made, invariably suitable dust load may have to be taken
Ans: The dust load may have to included under live load in situation as mentioned above. But this has to be specified either by client or in IS:875
Question: .it is better we include the Z purlin -.- S.Lakshmanan
Ans: Z purlins have to be designed based on either IS: 801 or the tables provided by manufacturer, which are developed based on test.
Question: .H section I beams are to be adopted in eqplaces.- S.Lakshmanan
Ans: Comment not clear
Question: For Industrial structures design, Crane load is considered as Occasional load since crane may not be operating with full capacity all the time. Hence while combining with Wind/Seismic loads, building structure is designed for either, \Reduced Wind/EQ load or Zero/reduced crane lifted load (Not wheel load) with full wind/Seismic load. These provisions are probabilistic in nature and varies across codes. For example Article 1612.3.2 of Section 1612 of UBC-1997 states "Crane hook loads need not be combined with roof live load or with more than three fourth of snow load or one half of the wind load". Load combination specified in Table 5.1 of IS: 800 Draft (Line 2) matches with above criteria where WL/EL factor is specified as 0.6 ( 1.2x 50 % WL) with full crane load Alternate to this combination is another case where full wind/Seismic load is combined with zero/reduced crane lifted capacity. IS: 800:1984 (Article 126.96.36.199) as well as IS: 800 draft (Article 3.5.5) makes statement " While investigating the effect of earthquake forces, the resulting effect from dead loads of all cranes parked in each bay positioned to cause maximum effect shall be considered." This means that along with seismic only (emphasis mine) dead loads of cranes shall be considered i.e. lifted load need not be considered. Going to Table 5.1 of IS: 800 Draft crane load factor specified is0.53 with full seismic load. To my understanding factor 0.53 is derived by 1.05 x 50 % crane wheel load. As we know wheel load is factor of (crab weight + bridge weight + lifted load) and only (crab weight + bridge weight) will not total to 50 % of maximum wheel load derived with full lifted capacity. This means part of lifted load is inbuilt in combination involving seismic load. This shall not be a problem except that article 3.5.5 from draft code shall be removed to avoid confusion. Also, since percentage of lifted load that gets inbuilt is unknown, determining transverse surge loads under this condition will involve some back calculation. Surge load is dependent only on crab weight and
lifted load, which needs to be extracted from wheel load calculated above In order to avoid this problem, a better solution will be to specify percentage of lifted load to be used with Wind/Seismic. I have come across some international norms, which specifies 50 % lifted load with wind and 20 % lifted load with seismic load. - Jignesh shah
Ans: We should debate this item and may be arrive at a factor like 20% eventually Industrial structures are alone candidates for steel construction in India and hence crane loads are important. - A R Chandrasekaran.
The code recommends use of reduced live load factor (1.2) when used with EL/WL. Further, an accompanying live load factor is further reduced in such a combination. In all these cases the crane load may be leading accompanying load, depending upon its magnitude relative to other live loads. As far the calculation of earthquake forces only dead load of crane is to be considered since the suspended load is not likely to experience the inertia force due to earthquake.
Question: Automated fabrication finds welding on only one side of the I section more economical & experiments have proven these to be effective. IS 800 is silent on the fabrication detail, even if some illustrations indicate the flange welded to both sides of the web-Sundar
Ans: The norm is to use fillet welds on both sides of the web, intermittent unless designed for fatigue .In thin walled construction used in Pre-engineered building weld from one side would usually be either partial or full penetration butt weld and is acceptable, provided distortion due to single side welding is avoided.
Question: Buckling behaviour (both local & overall buckling) of non-prismatic members (which are the norm in PEB) are not detailed in IS 800. What factors are to be used? -Sundar
Ans: The local buckling has to be checked using clauses associated with Fig 3.1 and table 3.1 for non-prismatic member also. The overall buckling of columns of non -prismatic section can be checked using equivalent slenderness ratio suggested in stability text books (Timoshenko and Gere). The lateral buckling of non-prismatic beams is dealt with in Appendix.F
Question: Most of the PEB systems rely on experimental values determined & published by MBMA for the entire system behaviour (including diaphragm action of the wall / roof cladding) and safety factors / coefficients used accordingly. This results in substantial savings in material & cost. This is part of the pioneering work done by an eminent Engineer of Indian origin in the US. Can these results be used as a basis to design systems, which deviate from IS 800? - Sundar
Ans: Yes, Refer Section: 14 Design Assisted by Testing
Question: May I request that some guidance on corrosion allowance and its implication on use of cold formed steel be included in IS 800. - (B. J. Gupta)
Ans: The corrosion protection measures in general are discussed in Section 15. The design of cold-formed steel members should be as per IS: 801. Nevertheless section 15 may be used for cold-formed steel members also.
Question: The definitions of INTERNAL ELEMENTS and OUTSIDE ELEMENTS defined in Clause 3.7.2 are not very clear. Can these to explained further using
figures / diagrams. -Amit
Ans: We will add a statement such as "web of I-section and flange and web of box section" internal elements and flange over hang of an I section stem of T section and legs of angle section" in outside elements.
Question: Refer to Note: 5 of Table 3.1. If r1 is the ratio of actual average axial compressive stress to design compressive stress of web alone and r2 is the ratio of actual average axial compressive stress to design compressive stress of overall section, then under what circumstances can the values of r1 and r2 be negative as indicated in Table 3.1 for web of I-H or box section? Please clarify. -Amit
Ans: r1 and r2 will be negative when the numerator of these ratios namely actual average axial stress is tensile in nature.
Question: For a section consisting of 2 Is' or 2 channels placed at certain distance centre to centre or back to back, what is the criteria to determine whether the compound section is plastic or compact or semi-compact or slender so that its capacity in bending in either directions can be estimated. This will be required specifically for columns of above sections subjected to compression and simultaneous bi-axial bending. -Amit
Ans: The classification of such built-up section be governed by the classification of individual sections.
Question: While as I agree with Prof. Chandrasekaran's point of allowing larger 'R' value for steel structures, I will like to draw attention to mismatch between IS: 800 and IS: 1893 in R values.
1. Ordinary moment frames (OMF) per IS:1893 (Table 7 item (1) i) is 3.0. Please read with foot note 20 which states frames detailed per IS: 456 or IS: 800, there by meaning this is applicable for steel frames also.
'R' value for similar frame is provided as 4.0 in Table 12.1 Sr no. 2 a) in IS:800 draft. While as it is understandable that for steel frame 4.0 is more logical value, per reason cited by Prof. Chandrasekaran below, the appropriate place to define it is IS: 1893 using which an engineer determines seismic forces. Since, IS: 1893 is already published, it makes sense to eliminate table 12.1 from IS: 800 draft-Jignesh
Ans: "Value of R in table 12.1 is to be used, if provisions of section 12 are followed. Also IS: 1893 does not specify R-values for designed as per LSM or Section 12
Question: The following clause is not clear
The definition in clause 16.2(a) ii states "Members with more than one face in contact
with a concrete or masonry floor or wall may be treated as three-sided fire exposure."
Does that mean the member (say a column) enclosed from all four sides by brickwork
would still be treated as three sided fire exposure??- Vijay Patil
Ans: For the purpose of fire exposure it is to be taken so conservatively. But the effect of
protection received due to enclosure of the member treated separately.
Question: Sub: Crane load combinations in draft IS:800
IS 875 (Part 2) indicates four classes of cranes and points to IS:807 for definition of the four classes of cranes. The probability of operating to full capacity is highest for class 4 cranes and lowest for class 1 crane. As per IS:807, a crane is classified as class 4 crane if (1) it is operated for atleast 500 hours per year; (2) lifted load is more than 2/3 rd of the safe load atleast 1000 times in a year and (3) the speed of operation of crab and crane is more than 100 meters per minute. The mean return period for wind load as per IS:875 is 50 years. The return period for our Himalayan earthquakes is reported to be about 100 years; and they last for less than a minute. The chances of simultaneous occurrence of full crane load along with either max wind load or max earthquake load can very well be imagined. Now, in section 1.2, of the draft IS:800, the "Accompanying load" is defined as the live load of lower magnitude which may act together with a leading imposed load. In an industrial structure, invariably, the crane load will be considered the main imposed load not leading when checking for collapse under wind/earthquake and the roof live load will be considered as accompanying imposed load. Referring to Table 5.1, it is seen that full crane load may have to be combined with either full wind load or with full earthquake load. This is not correct. The load combinations involving crane loads has been dealt with in detail in IS:4247 (Part 2) "Code of Practice for Structural Design of Surface Hydroelectric Power Station: Part 2: Superstructure". Crane loads have been considered as distinct from Live loads in this code.
Table 1 of above code gives increase in permissible stresses for 7 load combinations as follows:
(1) DL + LL + Moving crane, loaded to half capacity + Normal Tail Water Level: 0%
(2) DL + LL + Standing crane, loaded to full capacity + Normal TWL: 0%
(3) DL + LL + Moving crane, loaded to half capacity + Normal TWL + WL + Temp: 25%
(4) DL + LL + Moving crane, loaded to full capacity + Normal TWL + Temp: 25%
(5) DL + LL + Standing crane, unloaded + Normal TWL + EL: 33 1/3 %
(6) DL + LL + Moving crane, loaded to half capacity + Maximum TWL + Temp: 33 1/3%
(7) DL + Temporary or Construction load: 25%
Though IS 875 considers crane load and live load as part of imposed load, it will be more reasonable to separate out crane load from live load and other imposed loads. I suggest the following load combinations for limit state of strength:
(1) 1.5 DL + 1.5 LL + 1.5 CL (Moving crane, 50% lifted load)
(2) 1.5 DL + 0.75 LL + 1.5 CL (Moving crane, loaded to full capacity)
(3) 1.5 DL + 1.5 CL (Moving crane, 50% lifted load) + 1.5 WL
(4) 1.5 DL + 1.5 CL (Standing crane, unloaded) + 1.5 EL
(5) 0.9 DL + 0.9 CL (Moving crane, 50% lifted load) + 1.5 WL
(6) 0.9 DL + 0.9 CL (Standing crane, unloaded) + 1.5 EL
(7) 1.2 DL + 1.2 LL + 1.2 CL (Moving crane 50% capacity) + 1.2 WL
( 1.2 DL + 1.2 LL + 1.2 CL (Standing crane, unloaded) + 1.2 EL
(9) 1.2 DL + 0.6 LL + 1.2 CL (Moving crane, full capacity) + 0.6 WL
Load combinations containing erection loads and accidental loads can be as per the present draft.- S.P.Srinivasan
Ans: Same as the answer given earlier for crane load factor
.Question: Sub: Clause 3.7.2 in draft IS:800
I think that the paragraph "In such cases, the effective sections ..... section limit"
should be attached to "d) Slender ..... " itself .and should not be a separate paragraph
Question: The definition of average thickness of tapered elements may be given in this document itself, instead of referring to SP:6 -S.P.Srinivasan
Ans : The value depends on section profile and the actual average thickness are specified in the section handbook .
Question: I am unable to understand Table 3.1 "Limiting width to thickness ratio" fully.(1) The first item under the heading "Compression element" contains two expressions "Outstanding element of compression flange" and "Internal element of compression flange". There seems to be some error here. .- S.P.Srinivasan
Ans: "Outstanding element of compression flange" means compression flange of 'I' or "C" section, which is outstanding from web. For "I" section this values is half flange width. For box type closed section (rectangular or Square) compression flange is supported by two webs. For this case, portion of the flange inside webs is defined as "Internal element of compression flange". If same section has part of flange projecting beyond webs, that part shall be treated as "Outstanding element of compression flange"
Ans: The outstand width should be one half of total flange width I section, and width of plates between supporting plates in box section as shown in Fig 3.1
Question: The load factor for Notional Horizontal Loads is not defined anywhere. I suppose it should be same as that for DL and LL. Should we consider Notional Horizontal Load when considering crane loads (which themselves contain some horizontal loads) ? -S.P.Srinivasan
Ans: Your first understanding is right. Load factor for notional horizontal loads shall be same as DL &LL. These shall not be combined with other horizontal loads. See Article 188.8.131.52 b) which clearly states this.- Jignesh
Notional loads are to be used only under gravity load combination, in order to account for moments generated by sway of frames (P-D effect)
Question: The value of alpha as defined below the second expression for Tdn.(Clause 6.3.3 Single Angles) Alpha is defined as "0.6 for one or two bolts, 0.7 for three bolts, and 0.8 for four or more bolts in the end connection or equivalent weld length "How do we interpret "or equivalent weld length"? Equivalence between weld length and no of bolts will get influenced by diameter of bolts and by the throat thickness of the weld. If a welded joint is provided, how do we calculate alpha? After a more careful study of clause 6.3.3, I understand that Tdn, the design strength due to rupture of critical section is not applicable to welded joints since there are no holes at a welded joint. But I still cannot understand the presence of the term "or equivalent weld length" in the definition for alpha. S.P.Srinivasan
Ans: Clause 6.3.3 seems to be for tearing off of section and not for shear. Since in single angles only one leg is connected either by weld or by bolted joints diagonal tearing off of the connected leg alone might lead to rupture. The cross sectional area of plane of rupture may be less for single bolted joint and will increase with the number of bolts. Hence the variation of alpha from 0.6 to 0.8 is understandable. I think 0.8 should be for 4 bolts and above joints and for welded joints. -Narendrakumar.
Section 6.3.3 deals with failure of angles by tearing of net section at end connection, where shear lag may cause in the outstanding leg stresses less than ultimate stress. The first equation is the section in terms of b accounts for this effect more exactly. The second equation in terms of a is approximate and is to be used in preliminary design. In case of welds this will actually depend upon, if the welds are transverse, longitudinal or combined. Designer has to hence use an judgment to arrive at equivalent bolts
Question : I find that a foreword is missing. For a code, which recommends a change from the way we have been designing steel, this is a MUST. We are moving from ASD (or working stress design) to limit state design and various concepts need to be expanded. I am also not sure why we are not going into LRFD instead of Limit State. The foreword needs to elaborate the departures from the earlier IS 800-1984, the change in the philosophy of design and the whys and how is of it. Without this explanation and a concise summary of the changes proposed, it is very difficult to understand the full impact of this revision.-Alpha
Ans: Yes, foreword will be added. However detailed explanation and derivatives will not be in the foreword but in the commentary.
Question: SECTION 1
a) There is a very expanded terminology as compared to the IS 800-1984.
I had suggestions for the following definitions:
i) Compact Section: While the definition is quite succinct, it needs to be expanded in view of the importance of the concept being discussed. There may be an appendix elaborating the concept with a diagram showing the bending stress distribution for different classes of sections- Compact vs. semi-compact vs. Slender.- S.P.Srinivasan
Ans: This is given in section 3.7
Question: ii) Design Load/Factored Load - "A load value obtained by multiplying the characteristic load with a load factor, which is generally implies it can be less than one also greater than one."
The definition suggests that load factor is generally greater than 1.0 We know that this is not true in load combinations of dead with wind or earthquake and this part of the sentence ".(load factor), which is generally one" may be removed. .- S.P.Srinivasan
Ans: The statement is generally (not always) greater than one, which is true in all cases except when gravity load contributes to stability (see footnote in table 5.1). We can eliminate the " which is generally greater than one" from the definition.
Question: iii) Instability - "The phenomenon which leads to the inability of an element, member or a structure to carry further load resulting in lateral deflection to the direction of loading and reducing stiffness." There could be other reasons of instability than eccentric deflection and this part of the definition from "due to eccentric deflection lateral to.." may be deleted. .- S.P.Srinivasan
Ans: The word eccentric could be removed.
Question: iv) Period of Structural Inadequacy - This should be renamed as "Period of Structural Inadequacy for Fire"
Ans: Yes , we will say "under fire"
Question: v) Semi Compact Section- Comment same as for Compact Section
Ans: See section 3.7
Question: vi) Stability Limit State - A limit state corresponding to the loss of static equilibrium of a structure by excessive deflection transverse to the direction of predominant loads.
Again, the last part of the definition from "by excessive deflection.." may be, eliminated as loss of static equilibrium may occur due to other reasons also.-Alpha
Ans: Overturning is different from the buckling of frame referred to here.
Question: Section 2. 2.2.4 Properties:
I was happy to see that the physical properties have been added in a consolidated manner and one no longer has to scrounge around searching for them. The draft code has done away with conformance specifications for washers, concrete and other materials. I wonder why. I for one would have been happier if they had included more materials such as studs used in composite construction (such as flooring with metal decking and concrete topping).-Alpha
Ans: The code aims at giving guidelines and information for design of general construction in steel. Specifications for manufacture, erection, installation and for the production of proprietary patented items cannot be included. Neither can guidelines for design of specific structures or shapes be given. Studs and metal decking will be treated in IS: 11384.
Question: Section 3
"It is quite evident that the code writers would like LSDM to be the design methodology in the years to come and the intent of retaining ASD (WSD) is only to give transition time to people to switch over.
Clause 3.5 Load Combinations
I agree with Jignesh that the entire details for crane loading may be removed for here and reference be made to IS 875 part 2 for crane loadings. This should also include, as he has mentioned elsewhere, that some % of lifted load for wind and earthquake load needs to be considered as against the 3.5.5 clause implying that no lifted load need be considered. Also as Vipul has brought out, the IS 875 should specify the bumper impact loads therein.
On the same lines I think blast loading should be addressed separately in a code for blast resistant design and referenced herein.
Clause 3.7.2 .-Alpha
Ans: See the response to similar question answered earlier
Question: As Amit has stated, the terminology "internal elements" and "outside elements" need to be explained with figures. .-Alpha
Ans: See answer given earlier
Question: Table 3.1 Limiting Width to Thickness Ratios
This table is unnecessarily complicated and confusing and could be cleaned up to make it more readable. The reading material provided in the refresher course (organised by INSDAG, IE(I) etc. in some cities such as Mumbai) on Proposed Revision of IS 800 has a cleaner table (Table 10) for limits on Width to Thickness Ratios and perhaps this could be used in the code instead.-Alpha
Question: Comparison of Clauses 184.108.40.206 and 220.127.116.11 in Draft IS: 800 The clauses 18.104.22.168 and 22.214.171.124 are very similar. But clause 126.96.36.199 is more elaborate and covers two more cases, viz, roof truss bearing and column web connection. Is there any reason for omitting these two cases in clause 188.8.131.52?- S.P.Srinivasan
Ans; We will give reference to section 7.3.3 in section 184.108.40.206
Question: Notional Horizontal Loads in Draft IS:800
The notional horizontal loads (Clauses 4.3.6, 4.1.2), and 220.127.116.11) are mentioned only regarding sway stability of the frames. Am I correct in assuming that notional horizontal loads need not be considered in strength check? If they are to be considered only for sway stability check, the load factor should be 1.0?
Ans: `The sway stability check is done as per combined forces requirement of section 9.3, which is a strength check, where in sway moment due to gravity loads is accounted for using the notional horizontal loads
Question: Minor typo errors in Draft IS:800
(1) Table 7.2: Welded box sections: second expression below "Thick welds and" should be "h/tw" instead of "d/tw"-- S.P.Srinivasan
Question: Clause 18.104.22.168: The term "22.214.171.124" should probably read as "7.5.1"
Ans: No, Double angles on the same side of the gusset have the principle axis parallel and perpendicular to the gusset and hence will be designer not as per 7.5.1 , but as per 126.96.36.199
Question: Comparison of Clauses 188.8.131.52(b) and 184.108.40.206
Clauses 220.127.116.11 (b) and 18.104.22.168 are similar, but, in addition, clause 22.214.171.124 permits simpler (?) equal division of joint moment to upper and lower columns. I think the provision regarding equal distribution of joint moment to upper and lower columns is not necessary. In any case, (MI/length) has to be calculated to check whether this equal distribution is permissible. Once we have I/l values it is easy to apportion the joint moment in proportion to their stiff nesses, which is more accurate-- S.P.Srinivasan
Ans: We will remove recommendation in 126.96.36.199(b) and refer to section 188.8.131.52 analysis
Question: Clause 184.108.40.206 in Draft IS:800
The clause 220.127.116.11 gives the minimum size of base plate below stanchions. This clause is present in the 1984 code also. I do not understand the necessity of this provision. Is anything wrong in adopting smaller base plates, if the load transfer between stanchion and pedestal is otherwise proper?- - S.P.Srinivasan
Ans : This is recommended from practical consideration and ensure some minimum plate size relative to member size.
Question: Clause 18.104.22.168 and 22.214.171.124 in Draft IS:800
The two clauses 126.96.36.199 and 188.8.131.52 deal with the increase in effective slenderness ratio for laced and battened columns due to shear deformation effects. I wish to know whether the shear deformation effect affects only global slenderness ratio of the column or does it also affect the local slenderness ratio of the column ?- S.P.Srinivasan
Ans: The local slenderness ratio is not affected by shear deformation effect, just as single I section is not.
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