December 2010 

NASA/TM-2010-216876 

ARL-TR-5121 

Longitudinal Weld Land Buckling in 

Compression-Loaded Orthogrid Cylinders 

Robert P. Thornburgh 

U.S. Army Research Laboratory, Vehicle Technology Directorate 

Langley Research Center, Hampton, Virginia 

Mark W. Hilburger 

Langley Research Center, Hampton, Virginia 
NASA STI Program . . . in Profile

 Since its founding, NASA has been dedicated to 

the advancement of aeronautics and space science. 

The NASA scientific and technical information (STI) 

program plays a key part in helping NASA maintain 

this important role. 

 The NASA STI program operates under the 

auspices of the Agency Chief Information Officer. It 

collects, organizes, provides for archiving, and 

disseminates NASA’s STI. The NASA STI program 

provides access to the NASA Aeronautics and Space 

Database and its public interface, the NASA Technical 

Report Server, thus providing one of the largest 

collections of aeronautical and space science STI in 

the world. Results are published in both non-NASA 

channels and by NASA in the NASA STI Report 

Series, which includes the following report types: 

 TECHNICAL PUBLICATION. Reports of 

completed research or a major significant phase 

of research that present the results of NASA 

programs and include extensive data or 

theoretical analysis. Includes compilations of 

significant scientific and technical data and 

information deemed to be of continuing 

reference value. NASA counterpart of peerreviewed formal professional papers, but having 

less stringent limitations on manuscript length 

and extent of graphic presentations. 

 TECHNICAL MEMORANDUM. Scientific 

and technical findings that are preliminary or of 

specialized interest, e.g., quick release reports, 

working papers, and bibliographies that contain 

minimal annotation. Does not contain extensive 

analysis. 

 CONTRACTOR REPORT. Scientific and 

technical findings by NASA-sponsored 

contractors and grantees. 

 CONFERENCE PUBLICATION. Collected 

papers from scientific and technical 

conferences, symposia, seminars, or other 

meetings sponsored or co-sponsored by NASA. 

 SPECIAL PUBLICATION. Scientific, 

technical, or historical information from NASA 

programs, projects, and missions, often 

concerned with subjects having substantial 

public interest. 

 TECHNICAL TRANSLATION. Englishlanguage translations of foreign scientific and 

technical material pertinent to NASA’s mission. 

 Specialized services also include creating custom 

thesauri, building customized databases, and 

organizing and publishing research results. 

 For more information about the NASA STI 

program, see the following: 

 Access the NASA STI program home page at 

http://www.sti.nasa.gov

 E-mail your question via the Internet to 

help@sti.nasa.gov

 Fax your question to the NASA STI Help Desk 

at 443-757-5803 

 Phone the NASA STI Help Desk at 

443-757-5802 

 Write to: 

 NASA STI Help Desk 

 NASA Center for AeroSpace Information 

 7115 Standard Drive 

 Hanover, MD 21076-1320 
National Aeronautics and 

Space Administration 

Langley Research Center 

Hampton, Virginia 23681-2199 

 

December 2010 

NASA/TM-2010-216876 

ARL-TR-5121 

Longitudinal Weld Land Buckling in 

Compression-Loaded Orthogrid Cylinders 

Robert P. Thornburgh 

U.S. Army Research Laboratory, Vehicle Technology Directorate 

Langley Research Center, Hampton, Virginia 

Mark W. Hilburger 

Langley Research Center, Hampton, Virginia 
Available from: 

NASA Center for AeroSpace Information 

7115 Standard Drive 

Hanover, MD 21076-1320 

443-757-5802 

The use of trademarks or names of manufacturers in the report is for accurate reporting and does not 

constitute an official endorsement, either expressed or implied, of such products or manufacturers by the 

National Aeronautics and Space Administration. 
iii 

Preface 

The Shell Buckling Knockdown Factor Project (SBKF), NESC Assessment #: 07-010-E, was established 

in March of 2007 by the NASA Engineering and Safety Center (NESC) in collaboration with the NASA 

Constellation Program (CxP). The SBKF Project has the goal of developing and experimentally 

validating improved (i.e., less-conservative, more robust) shell buckling design factors (a.k.a. knockdown 

factors) and design technologies for launch vehicle structures. 

Preliminary design studies indicate that implementation of these new knockdown factors can enable 

significant weight savings in these vehicles and will help mitigate some of NASA’s future launch vehicle 

development and performance risks, e.g., reduced reliance on large-scale testing, high-fidelity estimates 

of as-built structural performance, increased payload capability, and improved structural reliability. 

To this end, a series of detailed Project Reports are being published to document all results from the 

SBKF Project and including design trade studies, test article and test facility design, analysis and test 

data, technology development white papers and state-of-the-art assessments, and finally shell design 

guidelines to update and/or augment the existing NASA SP series publications for the design of bucklingcritical thin-walled shell structures. A select group of significant results, in whole or in part, will be 

published as NASA Technical Memorandums (TM). 

Any documents that are published as a part of this series, that refer to or report specific designs or design, 

analysis and testing methodologies are to be regarded as guidelines and not as NASA requirements or 

criteria, except as specified in formal project specifications. 

Comments concerning the technical content of this NASA TM are welcomed. 

The following Project Report was used to create this TM: 

SBKF-P2-TR-2009-002
iv

Table of Contents 

Nomenclature ................................................................................................................................................ v

1.0 Introduction ...................................................................................................................................... 1

2.0 General Response of Welded Cylinders .......................................................................................... 2

3.0 Effect of Acreage Design ................................................................................................................. 7

4.0 Effect of Weld Land Design .......................................................................................................... 10

5.0 Effects of Local Details ................................................................................................................. 14

5.1 Influence of Adjacent Stiffeners ................................................................................................. 15

5.2 Ring Spacing ............................................................................................................................... 16

6.0 Minimizing the Effects of Weld Lands .......................................................................................... 17

7.0 Conclusion ..................................................................................................................................... 19

8.0 References ...................................................................................................................................... 20

List of Figures 

Figure 1.1. Typical axial weld land geometry for a cylindrical barrel. ........................................................ 2

Figure 2.1. Nomenclature used to define orthogrid geometry. .................................................................... 3

Figure 2.2. Predicted buckling mode shape for cylinder Design 1 using smeared stiffeners. ..................... 5

Figure 2.3. Predicted radial deformation caused by a 1-kip axial load for cylinder Design 1 using 

smeared stiffeners. ..................................................................................................................... 6

Figure 3.1. Predicted buckling loads for cylinders without axial weld lands. ............................................. 8

Figure 3.2. Predicted buckling loads for cylinders with axial weld lands. .................................................. 9

Figure 3.3. Reduction in buckling strength caused by axial weld lands. ................................................... 10

Figure 4.1. Predicted buckling loads for cylinder Design 1 with varying weld land geometry. ................ 11

Figure 4.2. Predicted buckling loads for cylinder Design 2 with varying weld land geometry. ................ 11

Figure 4.3. Predicted buckling loads for cylinder Design 3 with varying weld land geometry. ................ 12

Figure 4.4. Predicted buckling loads for cylinder Design 1 with varying weld land eccentricity. ............ 13

Figure 4.5. Predicted buckling loads for cylinder Design 2 with varying weld land eccentricity. ............ 13

Figure 4.6. Predicted buckling loads for cylinder Design 3 with varying weld land eccentricity. ............ 14

Figure 5.1. Predicted buckling mode shape for the detailed model of cylinder Design 1. ........................ 15

Figure 5.2. Influence of the distance between the axial weld land and the nearest axial stiffener. ........... 16

Figure 5.3. Effect of ring spacing on the buckling response along the axial weld land. ........................... 17

List of Tables 

Table 2.1. Dimensions (inches) and predicted buckling loads for specific orthogrid designs. .................. 4

Table 6.1. Predicted buckling loads for orthogrid designs with flanged reinforced stiffeners near the 

axial weld lands. ...................................................................................................................... 18

Table 6.2. Predicted buckling loads for externally stiffened orthogrid designs. ...................................... 19
v

Nomenclature 

Acronyms 

FE Finite Element 

LV Launch Vehicle 

OML Outer Mold Line 

STAGS Structural Analysis of General Shells 

List of Symbols 

br Ring Spacing 

bs Longitudinal Stiffener Spacing 

H Orthogrid Height 

h Stiffener Height From Skin 

L Cylinder Length 

Pcr Total Axial Load at Buckling 

R Cylinder Outer Mold Line (OML) Radius 

t Skin Thickness 

teff Effective Orthogrid Thickness 

tr Ring Thickness 

ts Longitudinal Stiffener Thickness 

W Radial Displacement of Cylinder Wall 

cr Average Axial Strain at Buckling 
Abstract 

Large stiffened cylinders used in launch vehicles (LV), such as the 

Space Shuttle External Tank, are manufactured by welding multiple 

curved panel sections into complete cylinders. The effects of the axial 

weld lands between the panel sections on the buckling load were studied, 

along with the interaction between the acreage stiffener arrangement 

and the weld land geometry. The relatively thick, unstiffened axial weld 

lands were shown to significantly reduce the buckling load when the 

cylinder is loaded in uniform axial compression, and a relationship 

between the reduction in buckling load and the orthogrid design is 

shown. Reducing the relative width of the weld lands is shown to be the 

most effective means of minimizing the reduction in buckling strength, 

and thicker weld lands are shown to not always increase their buckling 

resistance. Detailed cylinder models with individual stiffeners modeled 

as beams were used to show that the weld land buckling phenomenon 

was very sensitive to the specific location and geometry of stiffeners near 

the axial weld lands. It is also shown that the buckling load can be 

significantly improved by ensuring that the distance between the weld 

land and the adjacent longitudinal stiffener is minimized. 

1.0 Introduction 

Stiffened and unstiffened shells are very common in the structural design of aerospace vehicles and 

almost all other structures where weight is of primary concern. For these types of structures buckling is a 

critical failure mode that must be taken into account during the design process. Although some shells can 

buckle without catastrophic failure of the structure, many types of structures, such as large-diameter, thinwalled LV cylinders, must be designed to completely prevent buckling. Such structures exhibit an 

unstable buckling behavior in which the buckling event corresponds to a sudden loss in load-carrying 

capability. It is the design and analysis of this class of structures that is the topic of discussion in this 

paper. 

Integrally stiffened metallic cylinderical shell structures are an efficient design choice for LVs because 

their stiffness and strength can easily be tailored to create an optimal design for a given loading condition. 

Although stiffeners can be arranged in any arbitrary pattern, typically designers use either an isogrid 

arrangement [ref. 1], with the stiffeners forming equilateral triangular bays, or an orthogrid arrangement 

[refs. 26], with the stiffeners forming rectangular bays. The orthogrid arrangement is considered in this 

work, but the response of isogrid stiffener structures is fundamentally similar to the response of orthogrid 

structures. The fact that the stiffeners are integrally machined results in a reduction in stress 

concentrations and improved structural quality. By using metallic materials such as aluminum alloys, 

structural components can be welded together to form large structures such as liquid hydrogen tanks. 

However, in order to create the integrally stiffened cylinders needed to form most liquid fuel tanks, which 

are often 8 to 33 feet in diameter, multiple curved panels must be welded together along their longitudinal 

edges to form a single barrel component. Thus, the assembled structure is not a continuously stiffened 

shell, but rather a segmented shell with discontinuities created by the weld lands. The length and arcwidth of the panels used is governed by size of plate stock available for a given thickness, and often 

multiple barrels must then be welded together to create cylinders with the desired length. In the current 

state-of-the-art manufacturing process, panels are machined from flat plat stock to form the stiffeners on 

the inner surface of a thin skin before the panels are formed to the correct cylindrical radius. A weld land 

region is machined around the edges of the panel and the stiffeners are machined to taper down from their 

full height and blend into the weld lands, as shown in Figure 1.1. The weld lands are typically much 
2

thicker than the skin thickness used for the panel acreage, but the radius of outer surface of the weld land 

is often kept the same as the skin or outer mold line (OML). The thickness of the weld land is usually 

governed by the need to provide sufficient weld strength when subjected to internal pressure loads. The 

weld land width is dictated by the need to provide a sturdy surface to be used for clamping the panels in 

position during the welding process and allow clearance for the weld tool to travel along the weld line. 

The thickness of the skin between the weld land and the adjacent longitudinal stiffener is often increased 

to an intermediate thickness between the acreage skin thickness and the thickness of the weld land. This is 

done to reduce stresses in this region, but has little influence on the buckling strength of the cylinder, so 

this and other features, such as Dutton grooves [ref. 6], are not considered herein. 

Weld Line 

Axial Weld 

Land 

Longitudinal 

stiffeners 

Ring 

Figure 1.1. Typical axial weld land geometry for a cylindrical barrel. 

During initial design of the structure the presence of the weld lands is not taken into consideration, but as 

will be shown herein, weld lands can have a significantly adverse affect on the buckling strength of the 

cylinder.The objective of this work was to study the influence of the axial weld lands on the buckling of 

compression-loaded orthogrid cylinders. These weld lands are known to reduce the buckling loads of the 

cylinder relative to ideal cylinders without weld lands, but the mechanism by which this reduction is 

caused is not fully understood. The influence of the specific acreage and weld land geometry on the 

magnitude of the reduction was also studied. In addition, it is hoped that information can be provided to 

aid designers in minimizing the impact of the weld lands on the buckling strength of stiffened cylinder 

designs, and thereby reduce the structural mass of LV structures. 

2.0 General Response of Welded Cylinders 

In order to understand the influence of the axial weld lands on the response of orthogrid-stiffened 

cylinders subjected to axial compression, an analytical study was conducted using the Structural Analysis 

of General Shells (STAGS) finite-element (FE) code [ref. 7]. All cylinders presented herein have an outer 

radius, R, of 108 inches and an overall length, L, of 162 inches. The nomenclature used to define the 

orthogrid geometry is shown in Figure 2.1. It should be noted that most stiffener heights presented in this 

work are described in terms of the overall plate height, H, as opposed to the height as measured from the 

skin, h. The cylinders were all loaded by uniform axial-end shortening. This was accomplished by 

enforcing a zero-axial-displacement condition at one end, and constraining all nodes at the other end to 

have the same axial displacement as a single master node. A point force was then applied to the master 

node to apply an axial load to the cylinder. The loaded ends were assumed to have a clamped boundary 

condition, in which all nodal rotations and displacements were constrained at the ends. All cylinders were 

assumed to be made from an aluminum alloy with an elastic modulus of 11.0E6 psi, a Poisson ratio of 

0.33, and a density of 0.098 lbm/in3

. 
3

Figure 2.1. Nomenclature used to define orthogrid geometry.

Three types of FE models were used in this work: two that use a smeared stiffener assumption [refs. 3 and 

8] and one in which the stiffeners were approximated as beam elements attached to the skin. The first 

model based on the smeared stiffener assumption was a uniform cylinder without any axial or 

circumferential weld lands. This type of model was used as the baseline reference for the models with 

weld lands that will be compared. The effective or smeared stiffnesses for the stiffened skin were 

included via the smeared-stiffener shell wall construction capability within STAGS [ref. 7]. These models 

were all meshed with a uniform grid having 90 elements along the longitudinal axis and 360 elements 

around the circumference. This mesh size ensured that there were at least ten elements per half-wave for 

all of the linear eigen-mode shapes calculated, thus giving sufficiently converged FE predictions for the 

linear buckling loads of the ideal cylinders. The second model incorporated the axial weld land details, 

but still assumed smeared stiffener properties within the panel acreage. The mesh around the 

circumference of the cylinder was broken into segments based on the arc-width of the axial weld lands. 

Segments corresponding to weld lands were given shell wall properties based on the geometry of the weld 

lands, while the segments corresponding to the panel acreage were assigned smeared properties based on 

the orthogrid geometry, just as with the previous baseline model. The purpose of this model was to assess, 

in a general manner, how acreage design and weld land geometry interact within compression loaded 

cylinders. As will be shown later in this paper, the geometric details of the orthogrid stiffeners adjacent to 

the axial weld lands can have a significant influence on the response of the cylinder and make it difficult 

to effectively compare different cylinder geometries by using this simplified modeling approach. 

Specifically, by using smeared stiffener properties within the acreage, the influence caused by exact 

location of individual stiffeners is ignored; however, this influence can be captured by the third type of FE 

model, which has each discrete stiffener modeled. This model is described in detail in Section 5. 

To understand the response of a typical orthogrid-stiffened cylindrical shell a sample orthogrid design 

was first considered. The cylinder was first modeled with smeared stiffener properties, both with and 

without axial weld lands. The acreage geometry and dimensions are listed in Table 2.1 and is refered to as 

Design 1. The model with axial weld lands assumes that the cylinder is made from six identical panels, as 

would be typical for a cylinder of this size. The weld lands extend 2.0 inches to each side of the 

theoretical weld line, are 0.325-inch thick, and are flush with the outer surface of the skin or OML. When 

the in-plane and bending stiffnesses of the weld land were compared to the smeared values for the acreage 

one of the key problems with weld lands was quickly revealed. The weld land has an in-plane stiffness of 

H h 

t

br

bs

tr

ts
4

4.01E6 lb/in and a bending stiffness about its mid-surface of 3.53E4 in-lb. In contrast, the panel acreage 

has an effective axial membrane (in-plane) stiffness of 1.67E6 lb/in and an axial bending stiffness about 

its neutral axis of 1.91E5 in-lb. This means that the weld land membrane stiffness was over twice that of 

the acreage, but the bending stiffness was less than 20% of the acreage. Thus, when the cylinder was 

loaded with a uniform axial shortening, the local stress resultant was much greater at the axial weld lands, 

while at the same time the weld land has less bending stiffness to resist buckling. 

Table 2.1. Dimensions (inches) and predicted buckling loads for specific orthogrid designs. 

 Design 1 Design 2 Design 3 

t 0.100 0.140 0.060 

H 1.30 1.50 0.70 

br 7.0 7.0 9.0 

tr 0.100 0.140 0.060 

bs 3.0 4.0 3.0 

ts 0.100 0.140 0.060 

Smeared Pcr (kip) 3034 4898 698 

Smeared with Weld Land Pcr (kip) 2693 4326 599 

Reduction (percent) 11.2 11.7 14.2 

Detailed Model Pcr (kip) 2487 4146 564 

Reduction (percent) 18.0 15.4 19.2 

The predicted buckling load for the cylinder without axial weld lands is 3034 kips. The predicted linear 

buckling mode shape for this cylinder, shown in Figure 2.2 (a), is characterized by 4 axial half-waves and 

10 full waves around the circumference. Using a model with smeared stiffeners and including axial weld 

lands, the predicted linear buckling load was 2693 kips. This is an 11.2 percent reduction in load-carrying 

capability, in spite of the fact that the weld lands add 3.8 percent (64 lbs) to the mass of the cylinder. The 

predicted linear buckling mode shape, shown in Figure 2.2 (b), indicates that the buckling is concentrated 

along the weld lands. The influence of the weld lands is strong enough to change the displacement pattern 

into one that shows symmetry based on the six axial weld lands. 
5

(a) Without weld lands. 

(b) With axial weld lands. 

Figure 2.2. Predicted buckling mode shape for cylinder Design 1 using smeared stiffeners. 

There are other factors that contribute to the reduction in buckling load caused by the axial weld lands. 

Figure 2.3 shows the radial displacement for the cylinder, both with and without axial weld lands, 

subjected to a 1000-lb axial load, as calculated by a linear static analysis. In Figure 2.3 (a) the radial 

displacement shows the classic response for a compression-loaded cylinder, with a bending boundary 

layer at the ends transitioning into a uniform 2.93E-5-inch radial expansion for the majority of the length 

of the cylinder. The presence of the axial weld lands, however, changes the linear deformation of the 

cylinder and creates regions of inward deformation at the weld lands relative to the panel acreage, as 

shown in Figure 2.3 (b). The weld land exhibits significant coupling between axial compression load and 
6

circumferential bending which produces large inward bending stresses along the length of the axial weld 

lands. From the point of view of resisting buckling during axial compression, this type of deformation is 

very detrimental to the strength of the cylinder. As discussed above, the axial weld lands tend to attract 

stress and have reduced bending stiffness, and an inward deformation in this region only further reduces 

the buckling strength of the cylinder. Because the magnitude of this coupling is influenced by both the 

acreage geometry and the geometry of axial weld lands, it would be expected that, by varying the cylinder 

design parameters, the relative effect of the axial weld lands on the buckling load of the cylinder could be 

altered. 

(a) Without weld lands. 

(b) With axial weld lands. 

Figure 2.3. Predicted radial deformation caused by a 1-kip axial load for cylinder Design 1 

using smeared stiffeners. 
7

3.0 Effect of Acreage Design 

A parametric study was conducted on cylinders with axial weld lands in order to determine how acreage 

geometry influences the reduction in buckling load caused by the weld lands. The goal was to determine 

what parameters are most influential, and whether there are any trends that would provide designers with 

the ability to take into account the effects of the weld lands early in the design process. The linear 

buckling loads of cylinders modeled with axial weld lands and smeared stiffener properties for the panel 

acreage were compared to the buckling loads for models without weld lands. The use of the smeared 

models enable an assessment of how acreage design, as described by a small set of parameters, affects the 

buckling load without having to consider the effect of individual stiffener locations. 

The study was performed on a 108-inch radius cylinder with an overall length, L, of 162 inches. The 

cylinder was assumed to have six panels, with 0.325-inch thick weld lands that extend 2.0 inches to each 

side of the theoretical weld line and are flush with the outer surface of the skin. The four design 

parameters used were skin thickness (t), orthogrid height (H), longitudinal stiffener spacing (bs), and ring 

spacing (br). The ring thickness (tr) and longitudinal stiffener thickness (ts) were assumed in this study to 

be equal to the skin thickness, since there was no attempt made to take pocket buckling or stiffener 

crippling into consideration. The skin thicknesses used were 0.06, 0.08, 0.10, 0.14, and 0.18 inch. The 

orthogrid heights used were 0.70, 0.90, 1.10, 1.30, 1.50, and 1.70 inches. The longitudinal stiffener 

spacings considered were 3.0, 4.0, 5.0, 6.0, and 7.0 inches. The ring spacings used were 5.0, 7.0, 9.0, 

11.0, and 13.0 inches. This yields 750 combinations that span most of the practical design space for large 

orthogrid cylinders typical for LV designs. While some of the design parameters, such as the smaller 

values of H, might not seem appropriate for 108-inch-radius cylinders, they could be considered typical 

for larger (2730-foot diameter) designs scaled down to 18-foot diameter, since the thickness of some 

aluminum alloy plate stock is limited by manufacturing constraints. 

To compare the results for the different orthogrid geometries, an effective cylinder wall thickness was 

used. 

4

11 22

11 22 144

A A

D D

teff  (1) 

This thickness is essentially the ratio of bending stiffness to axial stiffness and can be thought of as 

representing the efficiency of the orthogrid design from a buckling standpoint. For reference, the axial 

buckling load for the cylinders without weld lands as a function of teff is shown in Figure 3.1. For a given 

skin thickness, the buckling load is approximately linearly proportional to teff. Designs on the left end of 

the graph would be typical in lightly loaded cylinders or very large cylinders with manufacturing limits. 

Designs on the right end are much more structurally efficient and heavily loaded. Many of these designs 

would not be practical in LVs because they would suffer from pocket buckling or stiffener crippling prior 

to general instability. For comparison purposes, the classical buckling prediction for an unstiffened shell 

wall is also shown. 
8

Figure 3.1. Predicted buckling loads for cylinders without axial weld lands. 

The addition of the axial weld lands resulted in a reduction of the linear buckling load in all 750 cases, 

with the reductions ranging in magnitude from 1.0 to 27.6 percent. The reduction in axial buckling load as 

a function of teff is shown in Figure 3.2. Although it was hoped that some overt trend would emerge, it is 

clear that no single parameter governs the effect of the axial weld lands on the axial buckling load. 

However, a careful examination of all of the results does reveal a number of trends. With all other 

parameters being equal, the reduction in buckling load increases with decreasing skin thickness. 

Similarly, the reduction in buckling load increases with increasing H, increasing bs, and decreasing br. 

Thus, the cylinder with t = 0.18 inch, H = 0.70 inch, bs = 3.0 inches, and br = 13.0 inches had the smallest 

reduction in buckling load (1.0 percent), although this is one of the least efficient and least practical 

designs. These trends do not bode well for designers, since optimal acreage designs generally involve thin 

skins, large stiffener heights, and smaller stiffener spacings. Designs with thicker skins probably have a 

smaller reduction in buckling load because the difference between the skin thickness and the weld land 

thickness of the skin is the primary source of the coupling between axial compression and circumferential 

bending that helps deform the weld land inward when subjected to axial compression. Designs with large 

stiffener heights logically suffer larger reductions in buckling load because the weld lands have even less 

bending stiffness relative to the acreage. The most useful of these trends is that axially stiff designs 

(bs < br) in general seem to be less affected by the presence of the axial weld lands than hoop stiff designs 

(br < bs) for a given nominal buckling load. However, even this trend has limits, as will be shown later. 
9

Figure 3.2. Predicted buckling loads for cylinders with axial weld lands. 

Since the weld lands, in general, have greater axial stiffness than the panel acreage, the total axial load at 

buckling may not be the ideal quantity for assessing the reduction of the buckling strength caused by the 

axial weld lands. If the weld lands increases the axial stiffness of the cylinder, it implies that for a given 

axial load the axial stress in the acreage is less than that of the corresponding cylinder without the axial 

weld lands. Thus, comparison of the average axial strain at buckling may be a better measure of the 

influence of the weld lands on the buckling performance of a cylinder. The reduction in the average axial 

strain at buckling as a function of teff is shown in Figure 3.3. The average axial strain is calculated as the 

ratio of the end-shortening displacement at buckling to L. As shown in Figure 3.3, the reductions in 

buckling strength calculated by using the average strain are 2 to 7 percent larger than the reductions in 

total axial load, but there is still no clear pattern with respect to teff. A similar trend can be seen for 

changes in H, t, br, and bs as was observed in the reduction in buckling load, but there is still no clear 

method available for estimating the reduction in buckling strength for a given acreage design without 

analyzing a model with weld lands present in it. 
10

Figure 3.3. Reduction in buckling strength caused by axial weld lands. 

4.0 Effect of Weld Land Design 

Next, three designs were chosen to study the effects of varying the weld land geometry. The details of the 

three designs are listed in Table 2.1 along with the predicted buckling loads with and without axial weld 

lands. Although none of these designs could be considered optimal, they are all relatively efficient and 

can be considered representative of the types of orthogrid designs used in modern LVs. The first design is 

the design discussed above, and represents a relatively efficient design with moderate load-carrying 

capability. The second design is representative of a very heavily loaded cylinder. The third design is 

representative of a lightly loaded structure or a scaled version of a very large diameter cylinder. In all 

three cases the design was chosen such that general instability would occur prior to local pocket buckling 

of the skin or crippling of the longitudinal stiffeners. 

For each of the three designs the weld land thickness and width was varied and the linear buckling load 

was calculated by using the weld land model with smeared stiffener properties in the acreage. The weld 

land thickness was varied between 0.15 and 0.40 inch, while the total width of the weld land was varied 

between 1.0 and 6.0 inches. The resulting buckling loads for the three acreage designs are shown in 

Figures 4.14.3. Designs 1 and 2 show similar trends; reducing the weld land width consistently increases 

the buckling strength of the cylinder, but the effect of the weld land thickness is dependent on the weld 

land width. For relatively narrow weld lands, increasing the thickness increases the buckling load of the 

cylinder, but for sufficiently wide weld lands there exists an optimal thickness for which the buckling 

load is a maximum. For the third acreage design the principle of reducing weld land width to increase 

cylinder buckling load still holds, but the effect of weld land thickness is different. For this design there is 

an optimal weld land thickness of approximately 0.20 inch for weld land widths less than 3.5 inches. For 

widths greater than this, increasing the weld land thickness increases the buckling strength of the cylinder.
11

Figure 4.1. Predicted buckling loads for cylinder Design 1 with varying weld land geometry. 

Figure 4.2. Predicted buckling loads for cylinder Design 2 with varying weld land geometry. 
12

Figure 4.3. Predicted buckling loads for cylinder Design 3 with varying weld land geometry. 

For the designer the consequences of this are clear; the width of the weld lands should be minimized to 

the limits permitted by manufacturing in order to maximize the buckling strength of the cylinder. Also, 

the designer should not assume that a thicker weld land adds strength to the cylinder. Nor should a weld 

land thickness be blindly selected without some analysis or historical design information to determine 

how thickness influences the buckling load for a particular acreage and weld land width combination. 

As discussed above the coupling between axial compression and circumferential bending in the weld land 

differs significantly from the orthogrid acreage. This difference can be changed by varying the location of 

the weld land mid-surface relative to the skin. Although this may not be practical from a manufacturing 

standpoint, it is valuable to understand the influence the weld land eccentricity has on the buckling 

response of compression-loaded cylinders. The three designs were analyzed with a varying combination 

of weld land thicknesses and eccentricities by using the weld land model with smeared stiffener properties 

in the acreage. The total weld land width was held constant at 4.0 inches, but the weld land thickness was 

varied between 0.15 inch and 0.40 inch The eccentricity of the weld land was varied between values of 

0.0 and 1.0, with 0.0 corresponding to the traditional arrangement of the outer surface of the weld land 

being flush with the outer surface of the skin and 1.0 corresponding to an arrangement where the weld 

land has been shifted radially outward so that the inner surface of the weld land is flush with the inner 

surface of the skin. 

The resulting buckling loads for designs 1, 2, and 3 are shown in Figures 4.44.6, respectively. These 

results indicate that regardless of the weld land thickness, shifting the weld land outward increased the 

buckling load for all three designs. For designs 1 and 2, this increase was approximately 10 percent for a 

0.325-inch-thick weld land, and for design 3 the increase was approximately 20 percent. There was only a 

slight change in the linear out-of-plane deformation created by the uniform axial compression, but the 

resulting mode shapes showed much less localization along the axial weld lands. This effect would be 

very beneficial to take advantage of from a buckling design point of view, but the manufacturing of such 

a panel would require almost the entire outer surface of the panel to be machined, which increases cost 

and may complicate the forming of the curvature into the panels. 
13

Figure 4.4. Predicted buckling loads for cylinder Design 1 with varying weld land eccentricity. 

Figure 4.5. Predicted buckling loads for cylinder Design 2 with varying weld land eccentricity. 
14

Figure 4.6. Predicted buckling loads for cylinder Design 3 with varying weld land eccentricity. 

5.0 Effects of Local Details 

All analysis described up to this point has used models with the effect of the stiffeners incorporated by 

use of smeared acreage properties. While this permits an inspection of the interaction between the 

orthogrid design and the influence of the axial weld lands, it omits local effects caused by the exact 

locations of the individual stiffeners adjacent to the weld lands. As will be shown, these effects can be 

significant, but local tailoring of the stiffener configuration can be used to improve the buckling load of 

the cylinder. 

The model used to study these effects uses shell elements to model the cylinder skin and includes both the 

longitudinal stiffeners and rings by means of STAGS’s discreet stiffener feature [ref. 7]. In STAGS the 

stiffeners are modeled as beam elements and coupled to the nodes that comprise the cylinder skin mesh. 

In addition to the axial weld lands, a 2.0-inch-wide circumferential weld land was added at each end of 

the cylinder to simulate the typical means used to join cylinder barrels together. The overall length 

remained 162 inches, and these weld lands simply reduced the axial length of the panel acreage. The weld 

lands were included by changing the shell wall properties for the elements that represented the weld 

lands. A mesh size of approximately 0.5o was used around the circumference and approximately 

1.2 inches was used axially. The exact mesh spacing varied as necessary to align nodes with stiffener 

locations and the edges of the weld lands. 

The predicted buckling loads for the detailed models of designs 1, 2, and 3 are 2487, 4146, and 564 kip, 

respectively (kip = 1000 lbf). This corresponds to a reduction from the nominal buckling load without 

weld lands of 18.0, 15.4, and 19.2 percent, respectively. All three designs show a larger reduction in 

buckling load than the models with smeared acreage properties, so clearly the refined modeling details 

can have a significant influence on the response of the cylinder with weld lands. When the buckling mode 

shapes are examined, the mode shapes predicted by the detailed model typically show more localization 

along the axial weld lands. An example of this can be seen in Figure 5.1, which shows the buckling mode 
15

shape predicted by the detailed model of design 1. The buckling mode shape for the detailed model shows 

much less deformation in the acreage away from the weld land than the corresponding model with 

smeared stiffeners and axial weld lands (Figure 2.2 (b)). This design case also shows another change that 

was often observed in the detailed models, which is an increase in the number of axial half-waves in the 

mode shape compared to the models with smeared acreage properties. 

Figure 5.1. Predicted buckling mode shape for the detailed model of cylinder Design 1. 

5.1 Influence of Adjacent Stiffeners 

When going from a smeared acreage design to a detailed design that accounts for each individual 

stiffener, one of the primary issues the designer is faced with is where to place the first stiffener adjacent 

to the weld land. Longitudinal stiffeners and rings typically have transitions where they taper down from 

their full height to the blend into the weld lands, so the designer is limited in how close the weld land can 

be to the adjacent parallel stiffener and not interfere with the transition detail. Typically, the pocket 

formed between the adjacent stiffener and the weld land is roughly the spacing used between individual 

stiffeners. However, since axial weld land buckling is dominated by local deformation along the weld 

land, it is expected that the exact location of the adjacent longitudinal stiffeners will influence the 

buckling load of the cylinder. 

To study this effect, the detailed models of the three cylinder designs were modified by increasing the 

longitudinal stiffener spacing to move the location of the adjacent stiffeners closer to the axial weld lands. 

Although it is somewhat counter-intuitive, the objective of this is to see if the buckling load of the 

cylinder can actually be increased by increasing the stiffener spacing. Since no stiffeners were added, the 

mass of the cylinder remained constant. The results of this study are shown in Figure 5.2 with the 

predicted buckling load normalized by the buckling load of the cylinder with weld lands and smeared 

acreage properties. The points plotted on the right represent the results for the initial detailed models 

described above. The points plotted on the left represent the case where the first longitudinal stiffener 

isplaced at the edge of the weld land. The resulting longitudinal stiffener spacing within the acreage for 

this case is 3.12 inches for designs 1 and 3, and 4.20 inches for design 2. These results show that the 

designer can increase the buckling load by moving the stiffeners closer to the axial weld lands even 

though this means increasing the spacing between the longitudinal stiffeners in the acreage. Interestingly, 

the effect seems to taper off within a certain distance from the weld land. Practically speaking, this should 
16

not be an issue, since the designer must allow a minimum distance between the weld land and the 

adjacent stiffener for the rings to taper down and blend into the weld land.

Figure 5.2. Influence of the distance between the axial weld land and the nearest axial stiffener. 

5.2 Ring Spacing 

Another effect that was observed when creating detailed models using discrete stiffeners was that there is 

a limit to which the ring spacing can be increased without adversely affecting the buckling load of the 

cylinder. As noted above, orthogrid designs with wider ring spacings tended to suffer slightly less 

reduction in buckling load due to the addition of the axial weld lands than designs with closely spaced 

rings. This assessment was based on models using smeared stiffener properties, but when this concept 

was tested with detailed models it proved to only be true up to a limiting value for the ring spacing. 

Above this limit the buckling loads were observed to drop rapidly. The detailed model of design 2 was 

used as a reference, and a study was performed in which only the ring spacing was changed. To eliminate 

any possible effects due to movement of the rings adjacent to the two ends of cylinder, the location of 

these two rings was held constant and the ring spacing was altered by varying the number of rings 

distributed between these two. Figure 5.3 shows the buckling load for the detailed models in this study 

along with the predicted buckling loads for the weld land models with smeared stiffener properties. For 

values of br less than or equal to 7 inches the detailed models show the same behavior as the smeared 

stiffener models, and the buckling mode shape, shown in Figure 5.3, shows the same large buckling 

deformations along the weld land. For ring spacing greater than 7 inches, the predicted buckling load 

drops sharply and the buckling mode shape has changed into a pattern in which the weld land is now 

buckling between the individual rings. Based on how sharply the buckling load drops, it is clear that an 

optimal cylinder design will need to maintain a ring spacing above this limiting value. Analysis of the 

other designs showed that this phenomenon is highly dependent on the acreage and weld land designs, 

and that it primarily manifests itself in heavily loaded cylinder designs. For the designer, a simple check 

of the buckling mode shape for a detailed model with discrete stiffeners is likely sufficient to ensure that 

this inter-ring weld land buckling is not occurring. 
17

Figure 5.3. Effect of ring spacing on the buckling response along the axial weld land. 

6.0 Minimizing the Effects of Weld Lands 

Based on the results above it is clear that the buckling load for compression-loaded cylinders with axial 

weld lands is very sensitive to local acreage stiffness adjacent to the weld land. A number of options to 

improve local bending stiffness are available to the designer. As discusses above, the first adjacent 

stiffener can be placed as close as practical to the weld land. Also, the longitudinal stiffeners close to the 

weld land can be reinforced to improve bending stiffness. Similarly, the longitudinal stiffener spacing can 

be tailored so that the stiffeners are more closely spaced near the weld land than they are towards the 

center of the panel. Local circumferential bending stiffness is also important and can be modified by 

reinforcing portions of the rings adjacent to the axial weld lands (e.g., make them thicker or add a flange 

to the top of the ring). Finally, a more radical option is to use an externally stiffened configuration which 

not only increases overall structural efficiency for the acreage, but also reduces the effect of the axial 

weld land on the buckling load. 

To demonstrate the effectiveness of reinforcing longitudinal stiffeners near the weld lands, designs 1, 2, 

and 3 were modified by adding a flange on the top of some of the longitudinal stiffeners adjacent to the 

axial weld lands and analyzed with the detailed modeling method. The original stiffener locations were 

used and the stiffener spacing was not altered to move the stiffeners closer to the weld lands. The flange 

added to the longitudinal stiffeners was flush with the inner edge of the stiffener so the overall stiffener 

height did not change. For each case the flange width was set equal to the orthogrid height, and the flange 

thickness was set equal to the stiffener thickness. Models were first analyzed with the flange added to 

only the nearest longitudinal stiffener on each side of the axial weld lands. Then models were analyzed 

with the flanges added to the nearest two and nearest three longitudinal stiffeners. 
18

The resulting buckling loads and improvement over the model without flanged stiffeners are shown in 

Table 6.1. The improvement in the buckling load varied between the three designs with design 2 showing 

approximately half of the improvement shown for designs 1 and 3. This is largely a result of the fact that 

design 2 has a wider stiffener spacing than designs 1 and 3 (4 inches vice 3 inches) and that in design 2 

the distance between the weld land and adjacent longitudinal stiffener is greater (2.55 inches vice 

2.05 inches). For all three designs, there were diminishing returns for the addition of flanges to more than 

the nearest stiffener, since the bending stiffness further away from the weld land has less influence on the 

weld land buckling phenomenon. Similar results can be obtained by increasing the thickness of the 

unflanged longitudinal stiffeners close to the weld lands, but this method adds less bending stiffness 

relative to the additional mass, so the improvements seen will be less. 

Table 6.1. Predicted buckling loads for orthogrid designs with flanged reinforced stiffeners 

near the axial weld lands. 

 Initial 1 Flanged Stiffener 2 Flanged Stiffeners 3 Flanged Stiffeners 

Design Pcr (kip) Pcr (kip) 

Improvement 

(percent) 

Pcr

(kip) 

Improvement 

(percent) 

Pcr

(kip) 

Improvement 

(percent) 

1 2487 2742 10.2 2793 12.3 2819 13.3 

2 4146 4305 3.8 4357 5.1 4406 6.3 

3 564 611 8.4 623 10.5 629 11.5 

The results above indicate that the buckling response can be heavily influenced by the stiffener geometry 

very close to the axial weld lands. Thus, the designer is severely constrained in how much the buckling 

load can be influenced if the stiffener spacing and thickness is held constant for the entire panel acreage. 

As was shown above, the benefits of moving the adjacent stiffener closer to the axial weld lands outweighed the impact of wider stiffener spacing in the panel acreage. By creating a non-uniform 

longitudinal stiffener pattern with more closely spaced stiffeners near the axial weld lands and slightly 

increasing the spacing away from the weld lands improvements can be made to the buckling load with 

little impact on the mass of the cylinder. Similarly, the thickness of the rings can be modified so that they 

are thicker near the axial weld lands while having the nominal thickness for the bulk of the panel acreage 

away from the weld lands. A trade study would need to be performed to assess the most effective use of 

additional structural mass near the weld lands for a particular cylinder design. 

Although it is conventional to have an internally stiffened geometry in LV structures, consideration 

should be given to using an externally stiffened arrangement. If the structure is to be covered with a 

sufficiently thick layer of insulating foam, there should be little aerodynamic effect caused by external 

stiffeners. The bending compression coupling that occurs in externally stiffened structures results in a 

more stable response when the cylinder is loaded in compression and significantly increases the buckling 

load. Table 6.2 lists the predicted buckling loads for externally stiffened versions of designs 1, 2, and 3 

based on the smeared model, smeared acreage and weld land model, and detailed model. For all three 

cases the outer radius of the skin was held constant and the stiffeners and weld lands were reflected to the 

external surface. These results show that the external stiffeners offer a 30- to 40-percent improvement in 

buckling strength over comparable internally stiffened designs. It can also be seen that the model with 

smeared acreage properties and axial weld lands predicts a smaller reduction in buckling load than the 

conventional internally stiffened models. This is because in the external configuration the bending 

stresses produced by axial compression are in the opposite direction resulting in an outward deformation 

along the axial weld lands. This pre-buckling deformation pattern is inherently more stable than the 

inward deformation seen in the internally stiffened cylinders and helps minimize the impact the weld land 

has on the buckling load. The large drop in buckling load seen for the detailed models is a result of the 

fact that since the acreage is so much more efficient the lack of bending stiffness adjacent to the weld 

lands becomes much more significant. The buckling mode shapes for the detailed models show a very 

narrow deformation pattern along the axial weld lands, so it is even more important in this arrangement to 
19

ensure longitudinal stiffeners are located as close as practical to the weld lands. However, even without 

any modification or reinforcement of the stiffeners near the axial weld lands, all three of the detail models 

for the externally stiffened cylinders predict greater buckling loads than the predicted buckling loads for 

the internally stiffened cylinder without weld lands. It should also be noted that the externally stiffened 

configuration is so much more efficient that these designs would likely exhibit local pocket buckling or 

stiffener crippling prior to global instability, so the cylinder would have to be redesigned to take full 

advantage of the external stiffener configuration. 

Table 6.2. Predicted buckling loads for externally stiffened orthogrid designs. 

 Smeared Smeared with Weld Land Detailed Model 

Design Pcr (kip) Pcr (kip) Reduction (percent) Pcr (kip) Reduction (percent)

1 4429 4077 8.0 3329 24.9 

2 7079 6532 7.7 5432 23.3 

3 932 888 4.7 821 11.8 

7.0 Conclusion 

The results presented herein show that the presence of axial weld lands in orthogrid cylinders can causes a 

significant reduction in the buckling strength when the cylinder is loaded in axial compression. Results 

show that minimizing the width of the weld lands is the most effective means to reduce the performance 

penalty associated with the axial weld lands. In addition, results have shown that the specific location of 

stiffeners near the weld lands has a direct impact on the weld land buckling phenomenon. Effort should be 

made to minimize the distance between the weld land and the adjacent longitudinal stiffeners, and adding 

flanges to these stiffeners has been shown to be highly effective in improving buckling load. 

Experience has shown that the amount of buckling load that can be recovered is highly dependent on the 

width of the axial weld lands. Since the manufacturing constraint on the width of the weld lands is usually 

independent of the cylinder radius, weld land buckling tends to be a more significant issue in smaller 

diameter LV structures than it is in large diameter ones. A 27-foot-diameter cylinder with a 4-inch total 

weld land width might be able to be reinforced with flanged stiffeners to remove almost all of the penalty 

in buckling load associated with the weld lands, while no practical amount of reinforcement might be able 

to improve the buckling load to better than 9095 percent of the nominal buckling load for a 18-footdiameter cylinder with 4inch-wide weld lands. It should be noted that the discussion in this work has 

focused on structural failure associated with global buckling caused by the axial compression. In practice, 

material stress limits and the stresses created by internal pressure also place constraints on the orthogrid 

design. While the goal for improving the buckling load is to minimize weld land width and arrange 

stiffeners to increase bending stiffness as close as possible to the weld lands, and local stresses may 

prevent the designer from achieving an optimal design from a buckling standpoint. 
20

8.0 References 

1. McDonnell-Douglas Astronautics Company: Isogrid Design Handbook. NASA CR-124075, 1973. 

2. Katz, L.: Compression Tests on Integrally Stiffened Cylinders. NASA TM X-53315, 1965. 

3. Singer, J.: “Buckling of Integrally Stiffened Cylindrical Shells – A Review of Experiment and 

Theory.” Contributions to the Theory of Aircraft Structures, 1972, pp. 325-357. 

4. Nemeth, M. P.; Britt, V. O.; Collins, T. J.; and Starnes, J. H., Jr.: Nonlinear Analysis of the Space 

Shuttle Superlightweight External Fuel Tank. NASA TP-3616, December 1996 

5. Nemeth, M. P.; Young, R. D.; Collins, T. J.; and Starnes, J. H., Jr.: Effects of Welding-Induced Initial 

Geometric Imperfections on the Nonlinear Behavior of the Space Shuttle Superlightweight LO2 Tank. 

39th AIAA/ASME/ASCE/AHS Structures, Structural Dynamics, and Materials Conference, Long 

Beach, California, 1998, paper # AIAA-98-1840. 

6. Ahmed, R.: Analysis of Stress Concentration in the Dutton Groove Regions of the Super Lightweight 

External Tank. NASA TM 108490, May 1995. 

7. Rankin, C. C.; Brogan, F. A.; Loden, W. A.; and Cabiness, H. D.: STAGS Users Manual, Version 

4.0. Lockheed Martin Missiles & Space Co., Inc., Advanced Technology Center, Report LMSC 

P032594, May 2001. 

8. Weingarten, V.; Seide, P.; and Peterson, J. P.: Buckling of Thin-Walled Circular Cylinders. NASA 

SP-8007, September 1965, revised August 1968. 
REPORT DOCUMENTATION PAGE Form Approved

OMB No. 0704-0188

2. REPORT TYPE 

Technical Memorandum

 4. TITLE AND SUBTITLE

Longitudinal Weld Land Buckling in Compression-Loaded Orthogrid 

Cylinders

5a. CONTRACT NUMBER

 6. AUTHOR(S)

Thornburgh, Robert P.; Hilburger, Mark W.

 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

NASA Langley Research Center U.S. Army Research Laboratory

Hampton, VA 23681-2199 Vehicle Technology Directorate

 NASA Langley Research Center

 Hampton, VA 23681-2199

 9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)

National Aeronautics and Space Administration

Washington, DC 20546-0001

and U.S. Army Research Laboratory

Adelphi, MD 20783-1145

 8. PERFORMING ORGANIZATION

 REPORT NUMBER

L-19960

10. SPONSOR/MONITOR'S ACRONYM(S)

NASA

13. SUPPLEMENTARY NOTES

12. DISTRIBUTION/AVAILABILITY STATEMENT

Unclassified -Unlimited

Subject Category - 16 Space Transportation and Safety

Availability: NASA CASI (443) 757-5802

19a. NAME OF RESPONSIBLE PERSON

STI Help Desk (email: help@sti.nasa.gov)

14. ABSTRACT

Large stiffened cylinders used in launch vehicles (LV), such as the Space Shuttle External Tank, are manufactured by welding 

multiple curved panel sections into complete cylinders. The effects of the axial weld lands between the panel sections on the 

buckling load were studied, along with the interaction between the acreage stiffener arrangement and the weld land geometry. 

This document contains the results of the studies.

15. SUBJECT TERMS

Axial weld lands; Orthogrid cylinders; Space Shuttle external tank; Compression loaded

18. NUMBER

 OF 

 PAGES

28

19b. TELEPHONE NUMBER (Include area code)

(443) 757-5802

a. REPORT

U

c. THIS PAGE

U

b. ABSTRACT

U

17. LIMITATION OF 

 ABSTRACT

UU

Prescribed by ANSI Std. Z39.18

Standard Form 298 (Rev. 8-98)

3. DATES COVERED (From - To)

5b. GRANT NUMBER

5c. PROGRAM ELEMENT NUMBER

5d. PROJECT NUMBER

5e. TASK NUMBER

5f. WORK UNIT NUMBER

869021.04.07.01.13

11. SPONSOR/MONITOR'S REPORT

 NUMBER(S)

NASA/TM-2010-216876 ARL-TR-5121

16. SECURITY CLASSIFICATION OF:

The public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, 

gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this 

collection of information, including suggestions for reducing this burden, to Department of Defense, Washington Headquarters Services, Directorate for Information Operations and 

Reports (0704-0188), 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person 

shall be subject to any penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number.

PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS.

1. REPORT DATE (DD-MM-YYYY)

01- 12 - 2010