Magazines

Civil War Field Fortifications

Magazines

Performance Considerations in the Design and Construction of Powder Magazines

A Brief Clarification of the Idea of Performance

All structures are designed and constructed to perform a more or less specific set of functions. A roof on an average house, for instance, is designed to protect both the interior spaces and the structural elements of the house from the destructive effects of weather. When a roof reflects the sun's heat back into the atmosphere, excludes rain and snow, and repels blowing wind it performs its function well. When that roof fails and starts leaking rainwater or loses its capacity to reflect heat it ceases to perform its designed function and has to be repaired or replaced. If the condition persists long enough the house itself will cease to perform its more general function of protecting its inhabitants and their possessions from the weather. There are, of course, a variety of reasons why a structure might cease to perform its designed function. A house designed for comfortable and healthful habitation by two people ceases to perform its designed function when the number of inhabitants increases beyond certain limits. If just one load bearing wall in the average house happens to be constructed using rotten wood or if its structural form and material composition are not strong enough to bear the weight of the roof the wall will begin to sag and induce abnormal stresses on other structural elements of the house that will eventually bring about a more generalized structural failure leading to ruination of the house. To put this in a very simplified form, a structure's performance refers to its designed and practical capacity to fulfill and continue to fulfill those conditions necessary for it to do the job it was intended to do.

Performance Design for Powder Magazines

Powder magazines in field fortifications had to be designed to provide the basic structural performance necessary to safeguard their contents against enemy artillery fire while creating an interior environment capable of preserving gunpowder in a serviceable condition. The three most important consideration in magazine design for storing powder were the exclusion of excessive moisture, proper ventilation, and storage capacity. Excessive moisture could destroy gunpowder rather quickly by decomposing and desolving of its base elements and causing caking of the grains. Moisture could be controlled by arranging for proper exterior drainage to carry both rain and ground water away from both the magazine and the entrance to the gallery and by properly sealing the roof of the interior structure. Ground water seeping into interior structure could be managed by sloping the ground surface subfloors toward the center of the chamber and toward passageway from the gallery to the chamber where the slope terminated in a deeper sump that was intended to catch the seepage. Water collecting in the sump could then be bailed out of the magazine. Seepage from the covering mass could also be managed by shaping the layers of rammed earth as the covering mass was being constructed. Water resistant tarpaulins could also be buried inside the covering mass of earth or placed on top of the interior structure to act as water blocks to force ground water absorbed into the covering mass to drain toward the exterior edges of the magazine. In cases where a magazine was subject to run-off from the fortification's terre-plein a trench could be excavated around the exterior of the covering mass. The trench itself would have to be prepared to drain the run-off into the fort's ditch.

Proper ventilation was necessary to achieve a beneficial exchange of air which would inhibit rot and the growth of destructive organisms, help manage dampness, and prevent the buildup of airborne chemical residues incident to the storage of large amounts of gunpowder packed in non-airtight containers within a small enclosed space. Rot and mildew, in particular, could destroy the wooden members of the magazine's structure and contaminate gunpowder in wooden barrels. Good ventilation was a great deal more desirable than it was achievable, especially in hastily constructed field works designed according to the engineering manuals most widely used during the Civil War. Fortunately these destructive forces work much more slowly than intrusive and excessive moisture and their effects only became a significant problem when a poorly ventilated magazine was used for a prolonged period of time. In cases where a magazine was expected to last more than a few months ventilator shafts leading through the covering mass could be included in the design. Small and heavily shuttered windows could also be included on the unengaged side of a magazine. The volume of space left free from obstruction was also important to gaining an efficient flow of air around the powder barrels and filled cartridges stored in a magazine. The barrels had to be stacked on their sides, with the upper tiers laid on runners that maintained separation between upper and lower barrels while an space between four and six inches had to be left clear between the stacked barrels and the magazine's walls.

Storage capacity was another important consideration in magazine design. Aside from being able to store gunpowder safely and in serviceable condition, a magazine had to have sufficient interior space to be able to keep a fortification's armament supplied for a more or less prolonged period of time. The capacity required largely depended on armament and the length of time that it was to be supplied. As the weight of the armament increased and the number of guns to be supplied from the magazine increased, the storage capacity of the magazine had to increase. An 8-inch Columbiad, for example, required a normal service charge of 10 pounds of powder each time it fired while a 10-inch Columbiad required 18 pounds of powder for each round. A magazine designed to hold enough powder to keep a battery of 10-inch Columbiads firing for several days would have to hold more powder and therefore have more interior space than a magazine designed to supply a similar number of 8-inch Columbiads firing for the same length of time. The number shells allotted to each gun that would be stored in the magazine and the number of filled cartridge bags needed to supply immediate or unexpected needs would also have to be included in the calculation of the interior space necessary for the magazine to adequately serve the fortification's armament.

Finally, the structural elements of a magazine's chamber and gallery had to be strong enough and put together well enough to sustain both the weight of the covering mass and concussions caused by the impact of shot and explosion of shells penetrating into the covering mass. The covering mass itself had to be thick enough to absorb impacts and keep shot and shell from penetrating the chamber and gallery and bringing about a catastrophic magazine failure. Engineering manuals of the period prescribed a variety of different designs that produced magazines capable of meeting performance requirements for safeguarding the chamber from enemy fire. These designs will be dealt with in some detail in the next section.

<<< Previous Page | Next Page >>>

General Introduction

Practical Designs Introduction

Magazine Failures

Rifle Pits Blockhouses Batteries

Back to Minor Works

Contents Home Page Major Works Siege Works Glossary

Mahan's Principles